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LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Class 


THE    SCIENCES 


A  READING  BOOK  FOR  CHILDREN 


ASTRONOMY,    PHYSICS  —  HEAT,    LIGHT,    SOUND, 

ELECTRICITY,  MAGNETISM  —  CHEMISTRY, 

PHYSIOGRAPHY,    METEOROLOGY 


BY 
EDWARD    S.   HOLDEN 


GINN   &   COMPANY 

BOSTON  •  NEW  YORK  •  CHICAGO  •  LONDON 


ENTERED  AT  STATIONERS'  HALL 


COPYRIGHT,  1902,  BY 
EDWARD   S.  HOLDEN 

ALL   RIGHTS    RESERVED 
68.10 


tgftc 


GINN    &   COMPANY  •  PRO- 
PRIETORS •  BOSTON  '  U.S.A. 


TO 
MY    YOUNG    FRIEND 

treble 


190795 


PREFACE 

THE  object  of  the  present  volume  is  to  present  chapters  to  be 
read  in  school  or  at  home  that  shall  materially  widen  the  outlook 
of  American  school  children  in  the  domain  of  science,  and  of  the 
applications  of  science  to  the  arts  and  to  daily  life.  It  is  in  no 
sense  a  text-book,  although  the  fundamental  principles  underlying 
the  sciences  treated  are  here  laid  down.  Its  main  object  is  to  help 
the  child  to  understand  the  material  world  about  him. 

All  natural  phenomena  are  orderly;  they  are  governed  by  law; 
they  are  not  magical.  1)hey  are  comprehended  by  some  one ;  why 
not  by  the  child  himself  ?  It  is  not  possible  to  explain  every  detail 
of  a  locomotive  to  a  young  pupil,  but  it  is  perfectly  practicable  to 
explain  its  principles  so  that  this  machine,  like  others,  becomes  a 
mere  special  case  of  certain  well-understood  general  laws. 

The  general  plan  of  the  book  is  to  waken  the  imagination ;  to 
convey  useful  knowledge ;  to  open  the  doors  towards  wisdom.  Its 
special  aim  is  to  stimulate  observation  and  to  excite  a  living  and 
lasting  interest  in  the  world  that  lies  about  us.  The  sciences  of 
astronomy,  physics,  chemistry,  meteorology,  and  physiography  are 
treated  as  fully  and  as  deeply  as  the  conditions  permit ;  and  the  les- 
sons that  they  teach  are  enforced  by  examples  taken  from  familiar 
and  important  things.  In  astronomy,  for  example,  emphasis  is  laid 
upon  phenomena  that  the  child  himself  can  observe,  and  he  is 
instructed  how  to  go  about  it.  The  rising  and  setting  of  the  stars, 
the  phases  of  the  moon,  the  uses  of  the  telescope,  are  explained  in 
simple  words.  The  mystery  of  these  and  other  matters  is  not  magical, 


VI  PREFACE 

as  the  child  at  first  supposes.  It  is  to  deeper  mysteries  that  his 
attention  is  here  directed.  Mere  phenomena  are  treated  as  special 
cases  of  very  general  laws.  The  same  process  is  followed  in  the 
exposition  of  the  other  sciences. 

Familiar  phenomena,  like  those  of  steam,  of  shadows,  of  reflected 
light,  of  musical  instruments,  of  echoes,  etc.,  are  referred  to  their 
fundamental  causes.  Whenever  it  is  desirable,  simple  experiments 
are  described  and  fully  illustrated,1  and  all  such  experiments  can 
very  well  be  repeated  in  the  schoolroom. 

Finally,  the  book  has  been  thrown  into  the  form  of  a  conversation 
between  children.  It  is  hoped  that  this  has  been  accomplished 
without  the  pedantry  of  Sandford  and  Merton  (although  it  must  be 
frankly  confessed  that  the  principal  interlocutor  has  his  knowledge 
very  well  in  hand  for  an  undergraduate  in  vacation  time)  or  the  sen- 
timentality of  other  more  modern  books  which  need  not  be  named 
here.  The  volume  is  the  result  of  a  sincere  belief  that  much  can 
be  done  to  aid  young  children  to  comprehend  the  material  world 
in  which  they  live  and  of  a  desire  to  have  a  part  in  a  work  so  very 

well  worth  doing. 

EDWARD   S.  HOLDEN. 

THE  CENTURY  CLUB, 
.   NEW  YORK  CITY,  January,  1903. 

l  Illustrations  have  been  reproduced  from  many  well-known  books,  especially  from  the 
reading  books  of  Finch  and  Stickney,  Frye's  geographies,  Davis'  physical  geography  and 
meteorology,  Gage's  text-books  of  physics,  Young's  text-books  of  astronomy,  etc.  To  the 
authors  of  these  works  the  writer  begs  to  express  his  sincere  thanks. 


CONTENTS 


PREFACE 


PAGE 
V 


INTRODUCTORY  CHAPTER    .    .    . 

BOOK  I.  ASTRONOMY,  —  The  Sci- 
ence of  the  Sun,  Moon,  and 
Stars  

The  Earth  as  a  Planet  .... 

Distance  of  the  Moon  from  the 
Earth 

Distance  of  the  Sun  from  the 
Earth 

The  Diameter  of  the  Earth    .     . 

Distance  of  the  Sun  from  the 
Earth  ......... 

The  Planets  Mercury  and  Venus 

The  Planets  Mars,  Jupiter,  Sat- 
urn, Uranus,  and  Neptune 

Distances  of  the  Planets  from  the 
Sun 

How  to  make  a  Map  that  shows 
the  Sun  and  Planets  .  .  . 

Scale  of  the  Map 

Sizes  of  the  Planets  compared  to 
the  Sun 

The  Solar  System;  the  Sun  and 
Planets 

Relative  Sizes  of  the  Planets 

The  Moons  of  the  Planets      .     . 

The  Minor  Planets;  the  Aster- 
oids   

Comets 

The  Stars    .  .... 


9 
9 

ii 
ii 

12 
14 

16 
16 

17 

i? 
18 


25 
28 

3° 

32 

32 
32 


Distances  of  the  Stars  .     ...     32 

What  is  a  Planet  ? 33 

Phases  of  the  Moon  (New  Moon, 

Full  Moon,  etc.) 34 

Number  of  the  Stars     ....     38 

Clusters  of  Stars 39 

The  Pleiades 39 

The  Milky  Way 41 

Do  the  Stars  have  Planets  as  the 

Sun  does  ? .42 

Shooting  Stars  ;   Meteors ;   Fire- 
balls      44 

The  Zodiacal  Light 46 

Nebulae 47 

Rising  and  Setting  of  the  Sun    .     48 
How  the  Sun  appears  to  move 

from  Rising  to  Setting   . 
The  Celestial  Sphere     .     . 
The  Northern  Stars       .     .     , 
The  Great  Bear  (the  Dipper) 
The  Southern  Stars       .     . 
Time  and  Timekeeping 

Telescopes 56 

A  Meridian  Circle 57 

The  Lick  Telescope      .     .     .     .     61 

The  Moon 62 

Mountains  on  the  Moon    ...     62 

Life  on  the  Planets 64 

The  Planet  Mars  .     .     .     .     .     .     64 

The  Planet  Jupiter 64 

Appendix  (Statistics  of  the  Solar 
System) 66-70 


49 
49 
5* 
53 
54 
56 


Vlll 


CONTENTS 


BOOK  II.    PHYSICS, — The  Science 
that    explains    Heat,    Light, 

Sound,  Electricity,  Magnetism  73 

Solids  and  Liquids 73 

Solids,  Liquids,  and  Gases  are 
made  up  of  Millions  of  Small 

Particles 74 

Heat  makes  Solids,  etc.,  expand  74 

Most  Gases  are  Invisible  ...  77 

The  Diving  Bell 78 

The  Earth's  Atmosphere  ...  78 

Balloons 80 

Air  is  Heavy 81 

Reservoirs,   Fountains,  and  the 

Water  Supply  of  Cities     .     .  81 

The  Barometer 83 

The  Air  presses  about  Fifteen 

Pounds  on  Every  Square  Inch  84 
How  to  measure  the  Heights  of 

Mountains 85 

The    Barometer   is    a    Weather- 
glass      86 

United  States  Weather  Bureau 

Predictions 88 

Thermometers      ......  88 

Steam 90 

The  Steam  Engine     ....  91 

The  Locomotive 94 

The  Steamship 96 

Light 96 

The     Sun's      Rays      travel      in 

Straight  Lines 96 

Shadows       101 

Eclipses  of  the  Sun  and  Moon  102 
Reflection  of  Light  .  .  .  .104 
Refraction  of  Light  .  .  .  .105 

Prism;  the  Spectrum      .     .     .  105 

Lenses 106 

Spectacles 107 


PAGE 

Sound no 

Velocity  of  Sound  and  Light  no 
Sound  is  a  Vibration      .     .     .112 
Musical     Instruments     (Bells, 
Pianos,     Violins,      Organs, 

Drums) 113 

Reflection  of  Sound  .     .     .     .116 

Echoes 116 

Musical  Notes 116 

The  Phonograph 117 

Electricity 119 

Apparatus  needed      .     .     .     .119 

Experiments 120 

Benjamin  Franklin's  Kite  .     .123 

Experiments 123 

Electric  Batteries 124 

The  Telegraph 125 

Telegraphic  Alphabet     .     .     .127 
Velocity  of  Electricity    .     .     .   1 28 

Magnetism 128 

Experiments 129 

Magnets 129 

Natural      Magnets     (Lode- 
stones)  133 

Electro-Magnets     .     .     .     .133 
Telegraph  Instruments  .     .     .133 

Electric  Bells 134 

The  Telephone 137 

The  Mariner's  Compass      .     .138 
The  Electric  Light     .     .     .     .140 

The  Dynamo 142 

Electric  Railways 143 

Appendix 144-147 

BOOK  III.  CHEMISTRY, — The  Sci- 
ence that  teaches  how  to  com- 
bine Two  Substances  so  as  to 
produce  a  Third  Substance  dif- 
ferent from  Either  .  .  .  .149 


CONTENTS 


IX 


Physical  Changes;  Solutions      .  150 

Mixtures 150 

Chemical  Combinations     .     .     -151 

Chemistry  (defined) 152 

Chemical  Affinity 152 

Gunpowder 153 

Bread  Making 1 54 

Composition  of  the  Air      .     .     .155 

Oxygen 155 

Nitrogen 155 

Combustion 156 

Hydrogen 157 

Balloons 157 

Water 157 

Chemical  Elements 158 

Metals 158 

Non- Metals 158 

Chemical  Compounds  .     .     .     .159 

BOOK  IV.   METEOROLOGY,  —  The 

Science  of  the  Weather       .     .161 
The  Atmosphere ;  the  Colors  of 

Sunset  and  Sunrise  .     .     .     .161 
Eruption  of  Krakatoa  (1883)       .  162 

Twilight 163 

Dust  in  the  Atmosphere     .     .     .163 

The  Rainbow 164 

Halos 1 65 

Fog  and  Clouds 165 

Dew 167 

Height  of  Clouds 167 

Rain 168 

Size  of  Raindrops 168 

Hail,  Snow,  and  Sleet  .     .     .     .168 
The   Snow  Line    (Line  of   Per- 
petual Snow) 1 68 

Snow  Crystals 169 

Uses  of  Snow 169 

Irrigation  of  Farming  Lands       .  169 


Frost 170 

Rainfall        170 

Rainfall  and  Crops 170 

Winds 171 

Wind  Vanes 171 

Force  of  the  Wind     .     .     .     .171 

Hurricanes 171 

Causes  of  the  Winds  .  .  .  172 
Land  and  Sea  Breezes  .  .  .174 

Weather      ,     . 174 

The  Seasons  (Spring,  Summer, 
Autumn,  Winter)  .     .     .     .175 

Storms 175 

Weather  Predictions  .  .  .176 
United  States  Weather  Bureau  176 
Storm  and  Other  Signals  .  .176 
Value  of  Weather  Predictions  178 
Summer  Thunderstorms  .  .  179 

Lightning 180 

Thunder 180 

Distance  of   a  Thunderstorm 

from  the  Observer       .     .     .   181 
Lightning  Rods 182 

BOOK  V.    PHYSIOGRAPHY,  —  The 
Science  of  the  Land  and  of  the 

Sea 185 

The  Oceans 185 

Depth  of  the  Sea  .    -..    .     .     .  186 

Soundings 186 

The  Sea  Bottom    .     .    .     .     .187 

Dredging 187 

Ooze 187 

Fish 188 

Phosphorescent  Fish  .  .  .188 
Deep-Sea  Fish  .  .  .  .  .  189 

Icebergs 189 

Glaciers 191 

Bowlders 191 


CONTENTS 


Pack-ice 191 

Ice- Worn  Rocks 192 

Rivers  and  Streams  .  .  .  .193 
Underground  Water  .  .  .193 
Meandering  Streams  .  .  .194 

Habits  of  Rivers 195 

Canons 196 

Flood  Plains 197 

Waterfalls 198 

The  Land 199 

Changes  in  the  Land      .     .     .199 
Mountains    sculptured    by 

Rains 200 

Sand  Dunes 200 

Waste  of  the  Land    .     .     .     .201 
Slow    Motions    of   the    Con- 
tinents        202 

Fossils 203 

Sandstones 204 

The  Interior  of  the  Earth  .     .  205 

Stratified  Rocks 205 

Formation      of      Mountain 

Ranges 205 

The     Oldest     Mountains     in 

America 208 

The  Age  of  the  Earth    .     .     .  209 
Age    of    Different     Parts    of 
America 209 


PACK 

Age  of  Man  on  the  Earth  .     .211 

Flint  Weapons 211 

The  Earliest  Drawing    .     .     .211 
The  First  Plaything  .     .     .     .212 

A  Geyser 213 

The  Internal  Heat  of  the  Earth  214 

Volcanoes 214 

Teneriffe 214 

Kilauea 215 

Vesuvius 215 

Herculaneum  and  Pompeii      .215 
Volcanoes  in  the  United  States  2 18 
Old    Lava    Fields   in    Idaho, 
Oregon,  and  Washington  .  218 

Earthquakes 218 

Cause  of  Earthquakes    .     .     .  219 
The    Charleston    Earthquake 

(1886) 219 

The  Mississippi  Valley  Earth- 
quake (1811) 222 

What  to  do  during  an  Earth- 
quake    222 

Earthquake  Detectors  —  how 

to  make  them 222 

The  Lisbon  Earthquake  (1755)  223 

Sea  Waves 224 

The  United  States  Ship  Wateree 
at  Iquique  (1868) 224 


THE    SCIENCES 

INTRODUCTORY  CHAPTER 

(To  be  read  by  the  children  who  own  this  book) 

LET  me  tell  you  how  this  book  came  to  be  written.  Once 
upon  a  time,  not  so  very  long  ago,  a  lot  of  children  were 
spending  the  summer  together  in  the  country.  Tom  and 
Agnes  were  brother  and  sister  and  were  together  all  the  day 
long ;  bicycling  or  playing  golf  in  the  morning,  reading  or 
studying  in  the  afternoon.  The  people  who  lived  in  the  vil- 
lage used  to  call  them  the  inseparables  because  they  were 
always  seen  together  during  their  whole  vacation  from  June  to 
September. 

Their  cousins  Fred  and  Mary  always  spent  a  part  of  every 
summer  with  them ;  and  when  they  came  there  were  four 
inseparables,  not  two.  The  children  liked  the  same  games, 
liked  to  read  the  same  books,  to  talk  about  the  same  kind  of 
things,  and  so  they  got  on  very  well  together ;  though  some- 
times the  two  boys  would  go  off  by  themselves  for  a  hard  day's 
tramp  in  the  hills,  or  to  shoot  woodchucks,  or  for  a  very  long 
bicycle  ride,  leaving  their  sisters  at  home  to  play  in  the  garden 
with  dolls,  or  to  do  fancywork  and  embroidery,  or  to  play 
tennis,  or  to  read  a  book  together.  Tom  was  thirteen  years 
old  then,  and  his  sister  Agnes  was  nine ;  cousin  Fred  was  ten 
and  his  sister  Mary  was  twelve. 

i 


2  THE  SCIENCES 

When  the  summer  afternoons  began  to  get  very  warm,  in 
July,  a  rule  was  made  that  the  children  should  spend  them  in 
the  house,  or  on  the  wide,  shady  porch,  or  else  under  the  trees 
on  the  lawn,  or  in  the  garden.  Golf,  tennis,  and  wheeling  had 
to  be  done  in  the  morning ;  the  afternoons  were  to  be  spent  in 
something  different.  Tom's  father  used  to  say  that  the  proverb 

All  work  and  no  play 
Makes  Jack  a  dull  boy 

was  only  half  a  proverb.     It  was  just  as  true,  he  said,  that 

All  play  and  no  work 
Makes  Jack  a  sad  shirk. 

And  so  a  part  of  every  summer  afternoon  was  given  up  to  read- 
ing some  good  book,  or  to  study,  or  to  work  of  some  sort.  The 
two  boys  had  their  guns  and  wheels  to  keep  thoroughly  bright 
and  clean,  and  a  dozen  other  things  of  the  sort ;  the  two  girls 
had  sewing  to  do ;  and  all  of  them,  together  agreed  to  keep  the 
pretty  garden  free  from  weeds. 

Almost  any  afternoon  you  might  see  the  four  inseparables 
tucked  away  in  a  corner  of  the  broad  piazza,  each  one  busy 
about  something,  and  all  talking  and  laughing  —  except,  of 
course,  when  one  of  them  was  reading,  and  the  others  paying 
good  attention.  Tom's  big  brother  Jack  was  at  home  from 
college,  and  in  the  afternoons  he  was  almost  always  on  the 
porch  reading,  or  else  on  the  green  lawn  lying  under  the  trees ; 
and  Tom's  older  sisters,  Mabel  and  Eleanor,  were  there  too, 
sewing,  or  embroidering,  or  reading,  or  talking  together. 

So  there  were  two  groups,  the  four  children  —  the  insepara- 
bles—  and  the  three  older  ones.  When  the  children  came  to 
something  in  their  book  that  they  did  not  quite  understand, 
Tom  would  call  out  to  his  big  brother  Jack  to  explain  it  to 


INTRODUCTORY   CHAPTER  3 

them,  and  Jack  would  usually  get  up  and  come  over  to  where 
the  children  were  and  tell  them  what  they  wanted  to  know. 
Almost  every  day  there  were  conversations  of  the  sort,  and 
explanations  by  some  one  of  the  older  ones  to  the  four 
children.  All  kinds  of  questions  would  come  up,  like  these  : 


FIG.  i .    THE  PORCH 

"Jack,  tell  us  why  a  'possum  pretends  to  be  dead  when 
he  is  only  frightened  and  wants  to  get  away." 

"Jack,  tell  us  why  a  rifle  shoots  so  much  straighter  than  a 
shot-gun  or  a  musket." 

"Jack,  what's  the  reason  that  a  lobster  hasn't  red  blood?" 
or  else : 

"  Eleanor,  what  is  the  difference  between  a  fern  and  a  tree  ? " 

"Is  that  coral  bead  made  by  an  animal  or  an  insect?" 

"What  is  amber,  anyway?"  and  so  on. 


THE   SCIENCES 


The  children  had  no  end  of  questions  to  ask,  and  Jack  or 
one  of  the  older  girls  could  generally  answer  them.  When 
they  could  not  give  a  complete  answer  the  dictionary  was 
brought  out ;  and  if  that  was  not  enough,  a  volume  of  the 
encyclopaedia.  Sometimes  the  questions  were  talked  over  at 
the  dinner  table  and  the  whole  family  had  something  to  say. 
Tom's  father  had  traveled  a  great  deal  and 
could  almost  always  tell  the  children  some 
real  "true"  story  —  something  that  had 
happened  to  himself  personally,  or  that  he 
had  read. 

The  chapters  in  this  book  are  conversa- 
tions that  the  children  had  among  them- 
selves or  with  the  older  people.  They  are 
written  down  here  in  fewer  words  than 
those  actually  spoken,  but  the  meaning  is 
the  same. 

When  the  children  were  talking  about 
electric  bells,  for  instance,  they  actually 
strung  a  wire  from  one  end  of  the  long 

It  costs  about  $1.10.    The 

two  wires  are  to  be  fastened    porch  to  the  other,  and  put  a  real  bell  at 

to  the  two  screw  posts  in      one    en£    Qf    jt    and    a    push    button    and    a 
the  picture  —  one  at  the     .  . 

left-hand  side,  and  one  in    battery  at  the  other.     In  this  book  there 

the  middle,  of  the  top  of    is  a  picture   showing  exactly  what  they 

did ;  but,  after  all,  you  cannot  understand 

an  electric  bell  half  so  well  by  a  picture  as  you  can  by  the 

real  bell  and  the  real  wire.1      So  when  one   of  the  children 

who  is  reading  this  book  comes  to  an  experiment  he  must  read 

all  that  the  book  says  about  it,  and  understand  it  as  well  as  he 

1  Children  should  be  careful  to  read  the  titles  printed  under  each  picture  with 
attention.     The  titles  explain  what  the  picture  means. 


FIG.  2.     A  CELL  OF 
DRY  BATTERY 


INTRODUCTORY   CHAPTER  5 

can.  If  he  can  get  an  electric  battery,  and  a  bell,  and  wire, 
and  a  push  button,  then  the  picture  in  this  book  will  tell  him 
exactly  how  to  join  them  together;  and  when  he  has  done  this 
and  actually  tried  the  experiment  —  and  made  it  succeed  —  he 
will  know  as  much  about  electric  bells  as  he  needs  to  know. 

If  he  cannot  get  the  bell  and  the  wire,  and  so  forth,  he  can 
probably  see  a  bell  of  the  sort  somewhere ;  and  if  he  keeps  his 
eyes  open  and  thinks  about  what  he  has  read,  he  can  certainly 
understand  how  it  works.  Here  is  the  battery  always  trying 
to  send  out  a  stream  of  electricity  along  any  wires  joined  to 
the  two  screws  at  the  top.  Here  is  the  wire,  which  is  almost 

Push 
Button 

Battery '    ' 1 

'Bell 


FIG.  3 

a  complete  loop  —  almost  but  not  quite.  If  the  loop  were  con- 
tinuous,—  if  the  wire  were  all  in  one  piece, — then  the  stream 
of  electricity  would  flow  along  the  wire  from  the  battery  and 
would  ring  the  bell. 

The  use  of  the  push  button  is  to  make  the  wire  continuous 

—  to  join  the  two  ends  of  it  so  that  the  stream  of  electricity 

can  pass  along  it.    When  you  have  done  this  —  when  you  have 

joined  the  ends  of  the  loop  of  wire  —  the  bell  rings,  and  only 

then,  which  is  just  as  it  should  be. 

This  book  gives  the  pictures  and  the  explanations.  They 
can  be  understood  by  paying  attention  ;  and  when  they  are 
once  understood  a  great  number  of  things  will  be  clear  that 


THE  SCIENCES 


all  children  ought  to  know,  and  that  have  to  be  learned  some- 
time.    Why  not  now  ?     The  sooner  the  better. 

If  you  read  what  is  written  in  the 
book  and  perfectly  understand  it,  that 
is  very  well.  If  there  is  an  experi- 
ment to  be  tried,  and  you  can  get  the 
things  to  try  it  with,  so  much  the  bet- 
ter. If  you  have  any  trouble  in 
understanding,  ask  some  one  —  your 
father,  your  mother,  your  teacher  — 
to  explain  to  you.  If  you  can  find 
another  book  —  a  dictionary  or  an 
encyclopaedia  —  that  describes  the 
same  experiment,  read  that  too. 
Perhaps  it  will  tell  you  what  you 
want  to  know,  better,  or  more  simply, 
or  more  fully,  or  in  a  different  way. 
Then,  finally,  keep  your  eyes  open  to 
actually  see  in  the  world  the  things 
that  are  talked  about  in  this  book. 
When  you  see  them  try  to  understand 
them.  Remember  what  you  have 
read  here,  and  you  will  find  that  you 
understand  a  good  many  things  that 
you  see  about  you  every  day.  Some- 
body understands  these  things,  — 
push  buttons,  electric  lamps,  tele- 
scopes, and  so  forth.  Why  should 
FIG.  5.  A  PUSH  BUTTON  not  you  ?  You  can  if  you  pay 
it  costs  thirty  cents.  The  two  attention  enough.  The  world  is, 

wires  are  fastened  to  two  screws  '     ,  .         T      .     . 

inside  the  push  button.  after  all,  your  world.     It  belongs  to 


FIG.  4.    AN  ELECTRIC  BELL 

It  costs  seventy-five  cents.     The 

wires  are  fastened  to  the  two 

screws  at  the  bottom  of  the  box. 


INTRODUCTORY  CHAPTER  7 

you  as  much  as  it  belongs  to  any  one.  The  things  in  it  can  all 
be  explained  and  understood.  It  is  everybody's  business  to 
try  to  understand  them  at  any  rate.  All  these  things  concern 
you.  The  more  you  know  about  them,  the  better  citizen  you 
can  be  —  the  more  useful  to  your  country,  to  your  friends,  and 
to  yourself. 


THE  MOON 
The  moon,  from  a  photograph  taken  with  the  great  telescope  of  the  Lick  Observatory. 


BOOK   I 
ASTRONOMY 

THE  SCIENCE  OF  THE  SUN,  MOON,  AND  STARS 


The  Earth  as  a  Planet. — The  children  were  looking  at  a  map 
of  the  world  one  fine  afternoon  and  studying  the  way  the  land 
and  water  are  distributed,  when  Agnes  said  :  "  I  never  knew 
before  how  little  land  there  was  on  the  earth.  Why,  there  is 
very  much  more  water  than  land."  "Oh,  yes,"  said  Tom, 
"there's  very  much  more  water  on  the  surface;  but  it's  all 
land  at  the  bottom  of  the  ocean.  The  sea  is  about  three  miles 
deep,  you  know,  and  then  you  come  to  the  ocean  bottom,  and 
that  is  solid  land  again.  The  earth  is  nearly  all  rocks  and  soil ; 
only  a  little  of  it  is  water,  after  all,  but  that  little  is  on  the 
surface,  of  course,  and  that  is  why  it  shows." 

Agnes.  So  the  earth  is  almost  all  land  ;  if  you  dig  down  deep 
enough,  you  would  come  to  rocks,  even  below  the  oceans  ? 

•  Tom.  Yes,  and  if  you  went  up  high  enough,  you  would 
come  to  nothing.  You  would  come  to  air  first,  and  then  by 
and  by  to  no  air,  and  then  you  would  come  to  just  nothing  — 
to  empty  space. 

Agnes.  Well,  it  is  n't  quite  empty,  as  you  call  it.  There 
are  other  globes  in  space.  There  are  other  planets,  and  the 
sun  and  the  moon,  and  there  are  simply  thousands  of  stars. 
So  space  is  n't  empty ;  it  is  pretty  full ! 

9 


FIG.  6.     AMERICA 


FIG.  7.     THE  OLD  WORLD 
10 


ASTRONOMY  1 1 

Distance  of  the  Moon  and  of  the  Sun  from  the  Earth. Here 

Tom's  big  brother  Jack  looked  up  from  his  book  and  said  : 
"  Well,  that  depends  on  what  you  call  full.  It  is  240,000  miles 
from  here  to  the  moon,  and  the  moon  is  the  very  nearest  of  all 
the  heavenly  bodies  to  us.  There  is  a  good  deal  of  empty 
space  between  us  and  the  moon,  it  seems  to  me." 

Agnes.  Two  hundred  and  forty  thousand  miles  !  Oh,  Jack, 
is  that  right? 

Jack.  Why,  that  is  n't  a  beginning  ;  how  far  off  do  you  sup- 
pose the  sun  is  ?  It  is  93,000,000  miles  —  millions  this  time, 


FIG.  8 

This  picture  shows  the  height  of  land  on  the  earth  compared  to  the  depth  of  the  sea.  If 
you  could  cut  the  earth  through  and  through  with  a  knife  and  look  at  one  part  only,  it 
would  look  something  like  the  picture.  All  the  shaded  part  \^\\  is  land.  The  curved 
line  drawn  all  across  the  picture,  near  the  top,  is  the  curve  of  the  surface  of  the  oceans. 
Part  of  one  of  the  oceans  is  shown  by  the  white  space  below  this  curved  line  and  above 
the  floor  of  the  ocean  itself,  —  the  shaded  land.  The  curve  of  the  ocean  surface  is  con- 
tinued across  the  picture  underneath  the  mountains.  If  the  surface  of  the  earth  were 
all  water,  the  bounding  line  would  be  this  curve.  From  side  to  side  of  the  picture  is 
about  350  miles.  If  the  whole  circle  of  the  earth  were  drawn,  it  would  be  about  eight 
feet  in  diameter.  That  is  the  scale  of  the  drawing. 

not  thousands ;  and  some  of  the  planets  are  much  farther  off 
yet,  and  every  one  of  the  stars  is  farther  off  still. 

Agnes.  Jack,  tell  us  about  it,  will  you  ?  We  don't  know, 
and  you  do. 

Jack.  The  very  first  thing  you  have  to  think  about  is  the 
size  of  the  earth.  How  far  is  it  through  and  through  the 
earth,  Tom  ?  If  you  pushed  a  stick  through  the  earth  from 
New  York  to  China,  how  long  would  the  stick  be  ? 


12 


THE  SCIENCES 


The  Diameter  of  the  Earth.  —  Tom.    The  geography  says  that 
the  diameter  of  the  earth  is  8000  miles ;  so  the  stick  would 


FIG.  9.    A  BALLOON 

Balloons  carrying  men  have  gone  up  more  than  five  miles,  and  small  balloons  carrying 
thermometers,  etc.,  have  been  sent  nearly  ten  miles  high.  The  atmosphere  of  the  earth 
extends  upwards  a  hundred  miles  or  so,  but  beyond  this  there  is  no  air  —  nothing  but 
empty  space. 

have  to  be  8000  miles  long,  —  as  long  as  from  Cape  Horn  to 
Hudson  Bay,  my  teacher  says. 


ASTRONOMY 


Jack.  That 's  about  right.  Suppose  there  were  a  railway 
from  Hudson  Bay  to  Cape  Horn,  and  express  trains  run- 
ning on  it  at  the  rate  of  40  miles  an  hour.  Let  us  see  how 
long  they  would  take  to  go  the  8000  miles.  They  would  go 


FIG.  10.    THE  FULL  MOON  RISING  IN  THE  EAST 

40  miles  in  one  hour,  and  80  miles  in  two  hours,  and  960  miles 
in  a  day —  say  1000  miles  a  day.  Well,  they  would  take  eight 
days  to  go  the  8000  miles,  then.  Now,  suppose  we  could 
build  a  railway  to  the  moon.  How  long  would  an  express  train 
take  to  go  the  distance  ?  Take  your  pencil,  Tom,  and  cipher 
it  out. 


THE  SCIENCES 


Tom.  You  said  the  distance  from  the  earth  to  the  moon 
was  240,000  miles.  If  the  train  goes  1000  miles  a  day,  it 
would  take  240  days.  I  don't  need  any  pencil. 

Jack.    Sure  enough ;  and  240  days  is  eight  months  (8  x  30 
=  240).     It  would  take  the  train  eight  months  to  go  from  the 
earth    to    the  moon,    then  —  eight  whole 
months,  traveling  night  and  day  at  forty 
miles  and  more  every  hour. 

Agnes.  I  should  be  nearly  a  year  older 
when  I  got  there  than  when  I  started, 
then. 

Jack.  Yes,  and  recollect  that  there  are 
no  stations  on  the  railway  to  the  moon. 
The  moon  is  the  heavenly  body  that  is 
nearest  to  us,  so  that  space  is  pretty 
nearly  empty,  after  all. 

Distance  of  the  Sun  from  the  Earth.  — 
Tom.    How  far  did  you  say  it  was  from 
the  earth  to  the  sun  —  93,000,000  miles  ? 
Jack.  That's  right.    You  will  need  your 

pencil  to  figure  out  how  long  the  express  train  would  take  to 
go  from  the  earth  to  the  sun,  Tom. 

Tom.  Yes,  it  is  like  this,  is  n't  it  ?  The  train  goes 
1000  miles  in  a  day;  then  it  will  take  93,000  days  to  get  to 

the  sun. 

30)93000    days 
12)  3100    months 
258^  years 

It  would  take  3100  months,  that  is  more  than  258  years,  to 
get  to  the  sun.  That 's  a  long  journey  !  You  would  have  258 
birthdays  on  the  road,  Agnes. 


FIG.  ii.    A  SCHOOL 
GLOBE 


ASTRONOMY  15 

Jack.  Put  it  this  way,  Tom  :  258  years  ago  takes  you  back 
to  the  year  1643  (1901—258=  1643).  The  Pilgrims  had  been  in 
New  England  only  twenty-three  years  in  1643,  for  they  came 
in  1620  (1643  —  1620  =  23).  Suppose  one  of  those  Pilgrims 


FIG.  12.     THE  PILGRIMS  LANDING  ON  PLYMOUTH  ROCK  FROM  THEIR  SHIP, 
THE  "  MAYFLOWER,"  DEC.  20,  1620 

to  have  stepped  on  to  the  train  at  Plymouth  Rock ;  he  would 
have  been  traveling  all  these  years,  and  he  would  only  have 
arrived  at  the  sun  a  few  years  ago ;  that  is,  if  he  had  lived 
to  make  the  journey. 

Tom.    Two  hundred  and  fifty-eight  years ! 


1 6  ,THE   SCIENCES 

The  Planets  Mercury  and  Venus.  — Jack.  Yes,  and  nearly 
all  that  space  is  empty  too.  There  are  only  two  planets 
between  the  earth  and  the  sun  —  Mercury  and  Venus. 

Agnes.    Venus,  the  evening  star  ? 

Jack.  Yes,  Venus  is  the  evening  star  sometimes.  Venus 
and  Mercury  are  the  only  planets  that  the  Pilgrim  would  pass 
on  the  road  from  the  earth  to  the  sun.  Space  is  rather  empty, 
is  n't  it  ? 

Agnes.  Are  n't  there  any  stars  in  between  the  earth  and 
the  sun,  Jack  ? 

Jack.  Not  one ;  the  real  stars  are  thousands  and  thousands 
of  times  farther  off.  We  call  Venus  the  "evening  star,"  but 
Venus  is  not  a  star  at  all,  but  a  planet.  Let  me  tell  you,  so 
that  you  can  make  a  sort  of  picture  of  it  all  in  your  minds. 
The  sun  is  there  in  the  middle  of  space  and  all  the  planets 
move  round  him,  just  as  the  earth  does.  Nearest  to  the  sun 
is  the  planet  Mercury,  and  then  comes  the  planet  Venus,  and 
then  the  planet  Earth. 

Agnes.  That  sounds  queerly  —  "  the  planet  Earth  "  —  though 
of  course  we  know  the  Earth  is  a  planet. 

The  Planets  Mars,  Jupiter,  Saturn,  Uranus, 1  and  Neptune.  — 
Jack.  Yes,  exactly  so.  And  then  there  are  other  planets 
farther  away  from  the  sun  than  the  earth  ;  Mars  for  one,  and 
then  Jupiter,  and  then  Saturn,  and  then  Uranus,  and  then 
Neptune.  That  is  all  we  know  of  ;  there  may  be  more  of 
them.  Neptune  is  thirty  times  as  far  from  the  sun  as  the 
earth  is.  Here  is  a  little  table  that  I  will  write  down  for  you 
to  keep.  You  need  not  memorize  it,  only  recollect  that 
Mercury  and  Venus  are  nearer  to  the  sun  than  we  are,  and 
that  all  the  others  are  farther  away. 

1  Pronounced  u'ra-nus. 


ASTRONOMY  17 

DISTANCES  OF  THE  PLANETS  FROM  THE  SUN 

The  planet  Mercury  is  36  million  miles  from  the  sun 

"  Venus       "  67  "  "  " 

"  Earth       "  93  "  "  " 

"  Mars        "  141  "  "  " 

"  Jupiter      "  483  "  "  " 

"  Saturn     "  886  "  "  " 

"  Uranus    "  1782  "  "  " 

"  Neptune  «  2791  "  "  " 

Jupiter  is  five  times,  and  Neptune  is  thirty  times,  as  far  from 
the  sun  as  the  earth  is. 

Tom.  Is  n't  there  a  map  of  all  these  planets  that  we 
can  see  ? 

Jack.  No,  and  there 's  a  good  reason  why.  Suppose  you 
tried  to  make  a  map  of  them,  and  suppose  you  took  the  dis- 
tance from  the  Sun  to  the  Earth  on  the  map  to  be  an  inch. 
Don't  you  see  that  the  distance  from  the  Sun  to  Neptune 
would  have  to  be  thirty  times  one  inch,  and  the  page  of  your 
book  thirty  inches  wide  —  nearly  a  yard  wide  ? 

Tom.  Of  course,  no  book  has  a  page  as  big  as  that ;  but 
you  might  make  little  maps. 

How  to  make  a  Map  that  shows  the  Sun  and  Planets.  — Jack. 
You  and  Agnes  can  make  a  map  yourselves  to-morrow  morn- 
ing, if  you  want  to,  when  you  go  out  for  a  walk,  and  I  '11  tell 
you  how  to  do  it. 

Suppose  you  take  the  large  globe  in  the  library,  that  you 
were  looking  at  just  now,  to  stand  for  the  Sun.  It  is  two  feet 
in  diameter.  Well,  the  diameter  of  the  real  Sun  is  870,000 
miles,  and  your  map  has  to  be  made  all  to  one  scale.  Every 
step  of  yours  is  about  two  feet  long,  is  n't  it,  Tom  ?  Try  it. 

Tom.    Yes,  my  steps  are  almost  exactly  two  feet  long. 


i8 


THE  SCIENCES 


Jack.  Well,  remember  to-morrow  that  every  step  you  take 
along  the  road  to  the  village  is  really  only  two  feet  long,  but 
that  it  stands  on  the  map  for  870,000  miles. 

Agnes.    Are  we  going  to  make  the  map  along  the  road  ? 


FIG.  13.    THE  ROAD  TO  THE  VILLAGE 

Jack.  My  dear,  you  have  to  do  it  that  way ;  your  map  is 
going  to  be  nearly  a  mile  and  a  quarter  long.  You  have  to  use 
the  whole  country  round  to  make  it. 

Agnes.    Well,  that  is  a  map  ! 

Tom.    How  shall  we  make  it,  Jack  ? 

Jack.  You  start,  you  know,  with  this  globe  in  the  house  to 
stand  for  the  Sun.  The  globe  is  two  feet  in  diameter,  and  the 
real  Sun  is  870,000  miles  in  diameter. 

Scale  of  the  Map. — "So,  recollect,  every  two  feet  on  your 
map  is  870,000  miles.  Every  one  of  your  steps,  Tom,  stands 
for  870,000  miles. 


ASTRONOMY  19 

"You  must  take  with  you 

a  very  small  grain  of  canary-bird  seed  to  stand  for  the  planet  Mercury ; 

a  very  small  green  pea  to  stand  for  the  planet  Venus; 

a  common  green  pea  to  stand  for  the  planet  Earth; 

a  rather  large  pin  out  of  Agnes'  work  box,  and  let  its  round  head  stand 

for  the  planet  Mars; 
an  orange  to  stand  for  the  planet  Jupiter; 
a  golf  ball  to  stand  for  the  planet  Saturn; 
a  common  marble  to  stand  for  the  planet  Uranus ; 
a  rather  large  marble  to  stand  for  the  planet  Neptune. 

Sizes  of  the  Planets  compared  to  the  Sun.  —  "If  this  globe, 
two  feet  in  diameter,  stands  for  the  Sun  (which  is  really  870,000 
miles  in  diameter),  then  a  common  green  pea  is  just  the  right 


FIG.  14 

The  sizes  of  the  planets  of  the  Solar  System  (the  Sun's  family)  compared  with  each  other. 
h  =  Saturn;  T/=  Jupiter;  tp=  Neptune;  &  =  Uranus;  <f  =  Mars  ;  C=  our  Moon; 
®=  Earth;  ?=  Venus;  $  =  Mercury. 


OF  THE 

UNIVERSITY 


20  THE  SCIENCES 

size  to  stand  for  the  Earth  (which  is  really  8000  miles  in 
diameter)  and  an  orange  is  just  the  right  size  to  stand  for 
Jupiter,  and  so  on.  You  are  going  to  carry  all  the  planets 
off  in  your  pocket,  and  when  you  have  put  them  down  in  the 
right  places  you  have  made  your  map." 

Tom.    How  shall  we  know  where  to  put  them  down  ? 
Jack.    I  will   give  you   the   right   number  of  steps  to  take 
between  the  Sun  and  every  one  of  the  planets.     If  one  of 
Tom's  steps  is  870,000  miles,  then 

Mercury   (the  canary  seed)  is  41   steps  from  the  Sun  (the  globe  at  the 

house) ; 

Venus  (the  small  pea)  is  77  steps  from  the  globe  that  stands  for  the  Sun ; 

Earth  (the  pea)  is  107                    "               "  «                    « 

Mars  (the  pin's  head)  is  162          "               "  «                    « 

Jupiter  (the  orange)  is  555             "               "  "                    « 

Saturn  (the  golf  ball)  is  1019        "               "  "                    " 

Uranus  (the  small  marble)  is  2048  "               "  "                    " 

ATeptune  (the  large  marble)  is  3208 "               "  "                    " 

Those  are  the  right  distances,  and  you  can  make  your  map 
to-morrow  morning  when  you  go  for  a  walk.  Recollect  that 
the  globe  in  the  house  stands  for  the  Sun.  You  are  to  walk 
away  from  it  along  the  road  to  the  village  until  you  've  taken  41 
steps.  Stop  there  and  put  down  the  canary  seed  to  stand 
for  the  planet  Mercury.  Then  go  on  36  steps  more  and  you 
will  be  77  steps  from  the  model  of  the  Sun.  This  will  be  the 
place  to  put  the  small  green  pea  that  stands  for  the  planet 
Venus  ;  then  go  on  30  steps  more  and  you  will  be  107  steps 
away  from  the  Sun.  This  will  be  the  place  to  put  down  the 
green  pea  that  stands  for  the  Earth,  and  so  on.  The  last 
planet  —  Neptune — will  be  3208  steps  away  from  the  house, 
—  about  one  and  a  fifth  miles  away. 


ASTRONOMY  2 1 

Agnes.  I  don't  believe  we  can  count  such  large  numbers, 
Jack ;  we  shall  be  sure  to  forget  them  and  lose  the  count. 

Jack.  True  enough,  Agnes.  Let  me  see  if  I  can't  make  it 
simpler  for  you.  I  will  write  down  on  a  card  all  that  you  have 
to  remember,  and  we  can  make  the  numbers  that  you  have  to 
count  smaller.  We  can  do  it  this  way  :  instead  of  counting 
the  distances  from  the  Sun  to  each  planet,  we  will  count  the 
number  of  steps  between  each  planet  and  the  next  one ;  this 
way. 

Here  is  the  card  that  Jack  wrote  : 


d         d^^ld         -id          tf/0;    00$          Wl 
/•         /  /> 

'i-e    •£££< 


<cz   <£&€&£   d.-£-€i< 


-e    -cz-t.d'Z-ti'W'C'e 

ff 


€ttd= 


4d    ^-    SS 


-id 
£e't  ^t-o- 


e  a--e-         -v-     i-f--  .  <t& 


<td 
i^td   <t-a    Cffle&trt&e   -id    44  '  £0 


22 


THE  SCIENCES 


NOTE.  —  The  numbers  that  are  needed  to  make  the  map  are  obtained  in  this 
way :  If  one  step  is  870,000  miles,  then 


The  distance  from  the  Sun  to  Mercury  = 
"  «  "    Venus     = 

"  "  "     Earth      = 

"  "  "     Mars       = 

u  u 


Differen 

4i  ste 

ps 

— 

77 

36 

107 

30 

162 

55 

555 

393 

1019 

464 

2048 

| 

1029 

3208      ' 

1 

1160 

36,000,000  miles: 

67,200,000  "  = 
92,900,000  "  : 
I4I,OOO,OOO  "  : 

Jupiter    =     483,000,000  "  = 

"  "  "     Saturn    =     886,000,000  "  = 

"  "  "     Uranus   =  1,782,000,000  "  = 

"  "  "     Neptune=  2,791,000,000  "  = 

In  the  last  column  are  the  differences  between  the  numbers  just  preceding;  77 
less  41  is  36,  107  less  77  is  30,  162  less  107  is  55,  and  so  on.  If  the  model  of  the 
planet  Mercury  must  be  41  steps  from  the  model  of  the  Sun,  and  if  the  model  of 
the  planet  Venus  must  be  77  steps  from  the  Sun,  then  the  model  of  Venus  must 
be  30  steps  away  from  the  model  of  Mercury,  and  so  on  for  the  others. 

When  the  next  day  came,  Tom  and  Agnes  set  out  to  make 
the  map  of  the  Sun  and  all  the  planets.  The  school  globe 
in  the  house  stood  for  the  Sun,  and  they  carried  the  models 
of  the  planets  with  them,  as  well  as  the  card  that  showed  how 
far  apart  the  planets  were  to  be  on  the  scale  of  their  map. 
Agnes  kept  the  card  in  her  hand  and  told  Tom  how  many 
steps  he  was  to  take.  At  the  house  she  said  :  "  Tom,  you 
must  take  41  steps,  and  then  stop."  So  Tom  walked  off, 
counting  his  steps  till  he  had  made  41,  and  then  he  put  down 
the  little  canary  seed  that  stood  for  the  planet  Mercury.  The 
globe  in  the  library  stood  for  the  Sun ;  this  tiny  seed  stood 
for  the  planet  Mercury ;  the  distance  from  the  globe  to  the 
seed  stood  for  the  real  distance  of  the  real  planet  Mercury 
from  the  real  Sun.  Thirty-six  steps  farther  they  put  down  the 
small  green  pea  that  stood  for  the  planet  Venus  ;  and  30  steps 
farther  still  they  put  down  the  green  pea  that  was  to  stand  for 
the  Earth. 

Here  they  stopped  for  a  minute  to  think  about  it  all.  This 
little  bit  of  a  green  pea  was  the  huge  Earth,  very,  very  much 


ASTRONOMY  23 

smaller  than  the  globe  that  stood  for  the  Sun.  They  could 
not  even  see  the  small  green  pea  that  stood  for  Venus,  nor 
the  little  seed  that  stood  for  Mercury,  though  they  knew  about 
where  they  were,  of  course.  There  were  no  other  planets  in 
the  real  space  between  the  real  Earth  and  the  real  Sun  except 


Mars 


esi  days 

FIG.  15 

A  plan  of  the  orbits  of  Mercury,  Venus,  the  Earth,  and  Mars. 

just  those  two,  Mercury  and  Venus,  and  space  was  almost 
empty,  after  all,  as  Jack  had  said,  except  for  few,  very  few, 
planets  that  were  exceedingly  far  apart.  "  Why,  we  can't  even 
see  the  models  of  Mercury  and  Venus  from  here,"  said  Agnes. 
"  No,"  said  Tom,  "  but  if  they  were  shining  things,  as  the 


24  THE   SCIENCES 

planets  are,  we  could  see  them.     They  ought  to  be  painted 
white  so  that  the  sunlight  would  make  them  glisten." 

So  the  children  went  on  putting  the  models  down  in  the 
road  at  the  right  distances  apart.  Agnes  read  the  right  num- 
bers from  the  card,  and  Tom  walked  away  counting  his  steps 

years  

Neptune 


Uranus 


A  plan  of  the  orbits  of  Mars,  Jupiter,  Saturn,  Uranus,  and  Neptune.     (The  scale  of  this 
drawing  is  much  smaller  than  that  of  the  preceding  one.) 

up  to  the  thousands.  He  got  rather  tired  of  it,  but  they  kept 
on  until  finally  all  the  models  were  put  down  at  the  right  dis- 
tances apart,  and  their  map  was  made.  By  this  time  they  were 
nearly  a  mile  and  a  quarter  away  from  home,  and  they  had 
spent  the  whole  morning  in  the  work.  But  the  work  was  not 


ASTRONOMY  25 

wasted.  They  really  understood  what  they  had  been  doing, 
and  realized,  as  very  few  people  —  even  grown  people  —  do, 
how  immensely  large  space  is,  and  how  few  —  very  few  — 
planets  there  are  to  fill  it.1 

When  the  children  came  home  that  day  there  was  a  great 
deal  of  talk  about  the  map  —  the  model  —  that  they  had  made. 
All  the  older  people  and  some  of  the  neighbors  were  interested 
in  it.  They  found  their  work  had  not  been  wasted  and  that 
they  had  really  learned  something. 

The  Solar  System;  the  Sun  and  Planets.  —  Jack  told  them 
some  interesting  things  about  the  sun  and  the  planets.  They 
knew  already,  of  course,  that  all  the  planets  moved  round  the 
sun  in  paths  that  were  called  orbits.  The  earth,  for  instance, 
goes  once  round  the  sun  every  year, —  every  365^  days.  Every 
one  of  the  planets  goes  round  the  sun,  too,  in  its  own  particular 
orbit,  in  its  own  year.  For  instance, 

Mercury  goes  round  the  Sun  in  88  days   =  about    3  months 

Venus  "  "  225  days    =      "        7        " 

Earth  "  "  365  days    =      "      12        " 

Mars  "  "  687  days    =      "      23        " 

Jupiter  "  "  12  years 

Saturn  "  "  29  years 

Uranus  "  "  84  years 

Neptune  "  "  165  years 

Tom's  father  told  them  about  one  of  the  kings  of  Spain  who, 
long  ago,  used  to  play  chess  on  a  huge  chessboard  with  real 
living  persons  for  chessmen.  These  men  moved  from  square 

1  It  is  strongly  recommended  that  the  teacher  should  make  such  a  model  of 
the  solar  system  as  has  just  been  described,  with  the  aid  of  his  pupils.  If  actually 
made,  it  will  lead  to  a  true  and  living  realization  of  the  dimensions  of  the  solar 
system.  No  amount  of  mere  class-room  instruction  can  do  this  for  young  children. 


26  THE   SCIENCES 

to  square  on  the  chessboard  as  the  game  went  on  ;  and  Tom's 
father  said  that  the  map  of  the  solar  system  with  its  eight 
planets  ought  to  have  had  eight  little  boys  who  would  walk  in 


FIG.  17 

In  this  picture  the  large  circle  stands  for  the  sun.  Each  of  the  small  dots  stands  for  the 
earth.  The  size  of  the  dots  and  of  the  circle  are  in  the  right  proportion.  It  would 
take  109  earths  in  a  row  stretched  across  the  disk  of  the  sun  to  reach  from  edge  to 
edge.  Count  them. 

circles  round  the  model  of  the  sun,  carrying  the  models  of  the 
planets  in  their  hands.  One  boy  would  carry  the  canary  seed 
that  stood  for  Mercury,  and  he  would  have  to  walk  once  round 
his  circle  in  three  months  ;  another  boy  would  carry  the  small 


ASTRONOMY  2^ 

green  pea  that  stood  for  Venus,  and  he  would  have  to  walk 
around  a  larger  circle  once  in  seven  months  ;  still  another  would 
carry  the  green  pea  that  stood  for  the  Earth,  and  he  would  have 
to  walk  around  the  circle  of  the  Earth's  orbit  once  in  each  year; 
and  so  on  for  all  the  other  planets.  The  boy  that  carried  the 


FIG.  1 8 

Three  drawings  of  Jupiter  as  seen  in  a  telescope.     The  lower  drawing  shows  Jupiter 
with  his  four  bright  satellites.     It  is  on  a  smaller  scale  than  the  others. 

marble  that  stood  for  Neptune  would  not  get  all  the  way  around 
his  circle  for  165  years.  "He  would  be  quite  grown  up  by 
the  time  he  got  round,  wouldn't  he?"  said  Agnes.  "Well," 
said  Jack,  "  Papa'  is  right ;  that  is  the  real  way  to  make  the 
model.  The  sun  is  in  the  middle.  All  the  planets  move  round 
him  in  circles;  each  one  of  the  planets  takes  a  different  time 


28  THE   SCIENCES 

to  go  once  around  its  orbit.      All  of   these  planets  together 
make  up  the  solar  system,  —  the  family  of  the  sun." 

Tom.  Why  do  they  call  it  the  solar  system,  Jack  ? 
Jack.  Just  because  it  is  the  sun's  system ;  sol,  in  Latin, 
means  "the  sun,"  and  solar  means  "  belonging  to  the  sun."  All 
the  planets  go  round  the  sun,  and  round  nothing  else.  That 's 
why.  The  sun  is  so  much  larger  than  any  of  the  planets,  or 
than  all  of  them  put  together  for  that  matter,  that  it  is  the 
sun's  system. 

Relative  Sizes  of  the  Planets.  —  "You  see,"  said  Jack,  "that 
the  sun  is  very  large  indeed.  He  is  as  much  larger  than  the 
earth  as  the  library  globe  is  larger  than  a  green  pea.  If  all 
the  solar  system  were  to  shrink  and  shrink  until  the  earth  — 
this  huge  earth  —  had  shrunk  to  the  size  of  one  green  pea,  the 
sun  would  still  be  as  big  as  the  globe  in  the  library  —  it  would 
be  two  feet  in  diameter." 

The  real  diameters  of  the  sun  and  planets  are  : 

The  Sun      is  866,400  miles  in  diameter 
Mercury       "       3,030  "  " 

Venus  «       7,700 

_,      _      .  I    The  smaller  planets 

The  Earth  "      7,918 

The  Moon  "      2,162 

Mars  "  4,230  "  " 

Jupiter  «  86,500  " 

Saturn  "  73,000 

Uranus  «  31,900  f  The  giant  planets 

Neptune      "    34,800 

"Oh  !"  said  Agnes,  "we  left  the  Moon  out  of  our  model." 
"  So  we  did,"  said  Tom  ;  "let  us  go  this  afternoon  and  stick 

a  pin  in  the  ground  to  stand  for  the  Moon,  alongside  of  the 

green  pea  that  stands  for  the  Earth." 


FIG.  19 

Drawings  of  the  planet  Saturn  as  seen  in  a  telescope  at  different  times.  In  the  upper  figure 
\ve  are  looking  at  Saturn's  rings  edgewise,  and  they  appear  as  a  thin  line.  In  the 
next  drawing  we  are  looking  down  on  the  rings.  In  the  third  drawing  -we  are  also 
looking  down  on  the  rings. 

29 


30  THE  SCIENCES 

The  Moons  of  the  Planets.  —  "Well,"  said  Jack,  "that's  all 
right.  Only  you  must  choose  a  pin  with  a  very  small  head. 
And,  while  you  are  about  it,  you  had  better  put  in  some  more 
pins,  for  several  of  the  other  planets  have  moons  —  satellites, 


FIG.  20.    THE  STARLIT  SKY 


they  are  called  —  and  they  go  around  their  planets  just  as  the 
Moon  goes  around  the  Earth.  Mercury  has  no  satellite  that  we 
know  of  ;  Venus  has  no  satellite  that  we  know  of  ;  the  Earth 
has  the  Moon  for  satellite  ;  Mars  has  two  very  small  satellites  ; 


FIG.  21.    THE  GREAT  COMET  OF  i 


32  THE    SCIENCES 

Jupiter  has  four  large  satellites  about  the  size  of  our  Moon,  and 
one  extremely  small  one  ;  Saturn  has  eight  satellites,  one  larger 
than  our  Moon  ;  Uranus  has  four  satellites ;  Neptune  has  one 
satellite  almost  the  same  size  as  our  Moon." 

The  Minor  Planets;  the  Asteroids.  —  "Yes,  and  at  the  same 
time  you  might  as  well  sprinkle  about  500  grains  of  sand 
in  the  space  between  Mars  and  Jupiter  to  stand  for  the  500 
minor  planets  that  they  call  asteroids.  There  are  about  500  of 
them  known  now,  and,  I  've  no  doubt,  hundreds  more  not  yet 
discovered.  When  you  read  in  the  newspaper  that  a  new 
planet  was  discovered  last  night  by  some  astronomer,  that 
means  that  another  one  of  these  minor  planets  has  been  found. 
They  find  them  by  photography  with  a  large  telescope." 

Comets.  —  "  And,  by  the  way,  put  in  two  or  three  thin  wisps 
of  cotton  wool  somewhere  to  stand  for  comets.  Comets  are 
mostly  made  out  of  shining  gas  —  they  are  n't  solid.  But 
they  look  a  little  like  wisps  of  cotton  wool,  anyway." 

Tom.    Is  that  all  ?     Shall  we  put  in  anything  else  ? 

Jack.  That  is  all  for  the  solar  system,  except  clouds  of  very 
little  stones,  almost  like  dust,  that  make  the  shooting  stars  or 
meteors. 

The  Stars.  —  "  What  about  the  stars  ?  "  said  Agnes. 

Jack.  Oh,  the  stars  are  not  part  of  the  solar  system,  Agnes ; 
they  are  millions  and  millions  of  miles  outside  of  it ;  the  very 
nearest  star  is  thousands  and  thousands  of  times  farther  from 
us  than  even  the  planet  Neptune. 

Tom.  How  far  off  are  they,  Jack,  anyway  ?  Could  we  get 
the  nearest  of  the  stars  on  our  model  ?  Where  would  it  be  ? 
In  the  next  county  ? 

Distances  of  the  Stars.  —  "  Let  me  see,"  said  Jack,  "the 
nearest  star  of  all  is  20,000,000,000,000  miles  from  the  sun  — 


ASTRONOMY  33 

twenty  millions  of  millions  of  miles !  If  you  were  to  put  it  on 
your  map,  it  would  have  to  be  about  9000  miles  from  where  we 
are  now  —  it  would  have  to  be  somewhere  in  China." 

Agnes.    Is  that  the  nearest  star,  Jack  ? 

Jack.  Yes,  the  very  nearest.  If  you  should  put  another 
school  globe  in  the  Chinese  emperor's  palace  at  Peking,  that 
would  stand  for  the  nearest  star  to  our  sun,  which  our  school 
globe  in  the  library  stands  for.  The  sun  is  a  star,  and  stars 
are  about  of  the  same  size.  So  a  school  globe  may  stand, for 
any  one  of  them. 

Tom.  Well,  space  is  empty  if  planets  and  stars  aren't  any 
closer  than  that.  What  is  the  difference  between  a  planet 
and  a  star,  anyway  ? 

What  is  a  Planet? — "The  greatest  difference,"  said  Jack, 
"  is  this  :  the  stars  shine  by  their  own  light,  just  as  an  electric 
street  lamp  shines ;  and  the  planets  shine  by  light  reflected 
from  the  sun,  just  as  a  football  would  shine  if  you  held  it  up 
in  the  sunlight." 

Tom.  Do  you  mean  that  Venus  and  Jupiter  do  not  shine  by 
their  own  light  ? 

Jack.  I  mean  just  that.  Venus  and  Jupiter  are  two  great 
globes  something  like  the  earth,  made  out  of  rocks  and  soil, 
with  clouds  all  around  them — clouds  something  like  our  clouds. 
The  sun  shines  on  them,  and  they  shine,  and  we  see  them.  If 
the  sun  were  to  stop  shining  on  them,  they  'd  go  out  like  a 
candle. 

Agnes.  But,  Jack,  Venus  shines  at  night,  in  the  dark  sky, 
when  the  sun  has  stopped  shining. 

Jack.  The  sun  has  stopped  shining  on  you  and  me  at  night 
because  the  earth  has  turned  round  and  we  are  in  the  earth's 
shadow ;  you  know  that.  But  all  the  while  the  sun  is  shining 


34  THE  SCIENCES 

just  the  same.  It  is  shining  on  the  other  side  of  the  earth,  where 
it  is  daytime,  and  it  is  sending  out  sunbeams  above  the  earth 
and  below  it,  everywhere  and  all  the  time.  Some  of  these  sun- 
beams fall  on  Jupiter  and  Venus  and  make  them  bright,  and 
we  see  them.  What  we  really  see  is  the  sun's  brightness 
reflected  back  to  us,  just  as  you  might  see  an  electric  light  at 
night  shining  on  a  mirror.  You  might  be  in  the  dark  yourself; 
the  electric  light  might  be  round  the  corner  of  the  street,  but 
the  mirror  would  be  bright. 

Tom.  So  planets  are  bright  because  the  sun  shines  on  them. 
Why  are  stars  bright  then  ? 

Jack.  Stars  are  bright  just  as  the  sun  is  bright.  The  sun 
makes  its  own  light  as  an  electric  lamp  makes  its  own  light. 
The  stars  are  like  the  sun.  They  shine  by  their  own  light. 
Planets  shine  by  borrowed  light.  They  borrow  their  light  from 
the  sun.  If  you  were  to  go  off  and  sit  on  the  nearest  star  and 
look  at  the  solar  system,  you  might  see  the  sun  in  the  middle 
of  it  shining  away  all  the  time  —  all  day  and  all  night,  too. 
And  if  you  could  see  our  little  group  of  eight  planets  wheeling 
around  it,  they  would  be  bright  on  the  side  nearest  the  sun 
—  on  the  side  shined  upon  ;  and  be  dark  on  the  side  away  from 
the  sun.  The  sunlight  cannot  go  through  them.  The  sun  can 
shine  only  on  that  part  of  a  planet  that  is  turned  towards  it. 

Phases  of  the  Moon  (New  Moon,  Full  Moon,  etc.).  —  "Don't 
you  know  the  moon  is  often  only  half  bright,  and  sometimes 
three-quarters  bright,  and  so  on  ?  Venus  looks  that  way  in  a 
telescope  sometimes ;  in  a  telescope  you  can  see  Venus  like  a 
crescent  moon  —  like  a  sickle.  You  do  not  see  it  like  that 
with  your  eye,  because  Venus  is  so  bright  that  your  eyes  are 
dazzled.  You  see  the  glare,  and  it  looks  like  any  other  daz- 
zling glare  ;  you  do  not  see  its  true  shape." 


ASTRONOMY 


35 


Tom.    You  can't  see  the  true  shape  of  a  sheet  of  tin  that 
the  sun  shines  on;   it  looks  just  like  a  dazzle  of  light. 


FIG.  22.    THE  NEW  MOON  SET- 
TING IN  THE  WEST 


FIG.  23.     THE  MOON  IN  THE 
FIRST  QUARTER 


FIG.  24.     FRED  WATCHING  THE  FULL  MOON  RISE  IN  THE  EAST 

Jack.  That  is  the  way  with  the  planets  when  you  do  not 
use  a  telescope.  Now  the  moon  looks  so  large,  and  the  light 
from  any  part  of  it  is  so  faint,  that  you  can  see  its  shape.  It 


36  THE  SCIENCES 

does  not  dazzle  your  eyes.  They  call  those  different  shapes  of 
the  bright  part  of  the  moon  \te  phases.  Venus  has  phases,  too. 
The  moon  is  a  globe,  you  know,  about  2000  miles  in  diameter. 
One  half  of  it  is  always  turned  towards  the  sun,  and  that  half 
of  it  is  always  bright,  day  and  night.  If  we  were  on  the  sun, 
we  should  always  see  the  whole  circle  of  the  moon  bright. 
But  we  are  on  the  earth,  and  the  bright  part  of  the  moon  is  not 


FIG.  25 

A  schoolroom  experiment  to  show  how  the  sun  lights  up  half  of  every  one  of  the  planets,  and 
only  half.  The  room  should  be  darkened ;  the  lamp  should  have  a  ground-glass  shade ; 
the  orange  that  stands  for  the  earth  or  planet  should  be  fastened  by  a  knitting  needle  to 
a  pincushion.  The  pupils  should  see  that  half,  and  only  half,  of  a  globe  (a  planet,  the 
earth,  the  moon)  is  illuminated.  They  should  also  see  that  by  going  to  different  parts 
of  the  room  different  portions  (phases)  of  the  illuminated  part  are  visible.  The  phases 
of  the  moon  can  be  explained  by  this  experiment.  Half  of  the  moon  is  lighted  by  the 
sun ;  all  of  the  illuminated  half  that  is  turned  towards  the  earth  is  seen  bright ;  the 
moon  moves  round  the  earth  and  turns  different  parts  to  it  at  different  times. 

always  turned  towards  us.  We  see  only  so  much  of  the  bright 
part  as  is  turned  towards  us  —  so  much  and  no  more. 

Agnes.  Sometimes  we  see  the  whole  circle  of  the  moon 
bright  —  at/w//  moon. 

Jack.  Yes,  we  see  it  so  when  the  sun  is  setting  in  the  west  and 
the  moon  rising  in  the  east.  The  sun  is  shining  full  on  the  moon, 
and  the  bright  half  of  the  moon  is  turned  full  towards  us. 


ASTRONOMY 


37 


Tom.    When  the  moon  is  a  sickle  it  is  often  in  the  west,  not 
far  from  the  sun  about  sunset. 
Jack.    That  is  the  phase  we  call  new  moon. 
Tom.    The  moon  goes  round  the  earth,  does  n't  it  ? 


FIRST    I 

•  f 

QUARTER      • 


IQUARTEH 


FIG.  26 

This  picture  shows  why  the  moon's  disk  has  different  shapes  at  different  times.  The  sun 
is  supposed  to  be  far  away  in  the  direction  of  the  top  of  the  page.  It  shines  on  the 
earth  and  lights  half  of  it.  It  is  night  on  the  unlighted  half  of  the  earth.  The  moon 
goes  around  the  earth  in  its  orbit  in  the  direction  of  the  arrow.  Wherever  the  moon 
is,  one  half  of  it  is  lighted  —  the  half  turned  towards  the  sun.  A  person  on  the 
earth  sees  one  half  of  the  moon  —  the  half  turned  towards  him.  The  little  circles  out- 
side the  orbit  in  the  picture  show  the  shape  that  the  bright  part  of  the  moon  will  have 
at  new  moon,  full  moon,  etc. 


38  THE  SCIENCES 

Jack.  It  goes  round  the  earth  once  in  every  month.  The 
moon's  month  begins  when  the  moon  is  a  new  moon.  Every 
night  the  bright  part  gets  larger,  and  in  about  a  week,  a  quarter 
of  a  month,  we  see  a  quarter  of  the  moon  bright ;  that  is  the 
first  quarter.  Two  weeks  after  the  new  moon  the  full  moon 
comes  ;  and  a  week  later  comes  a  moon  that  is  only  partly  bright 
again ;  that  is  the  third  quarter.  By  and  by,  in  four  weeks, 
comes  another  new  moon,  and  so  on  forever. 

Agnes.  One  of  my  storybooks  says  the  old  moons  are  cut  up 
to  make  stars  out  of.  They  would  n't  be  bright  enough,  would 
they  ? 

Jack.  Not  exactly.  Stars  are  the  brightest  things  there  are 
except  the  sun,  which  is  the  very  brightest  thing  we  know. 

Agnes.  There  are  faint  stars,  though  —  some  that  you  can 
scarcely  see. 

Tom.  They  are  faint  only  because  they  are  far  off.  If  you 
were  near  them,  they  would  be  bright  like  the  sun. 

Jack.  That 's  right.  The  stars  are  suns,  and  our  sun  is  a 
star.  All  of  them  are  really  very  much  alike,  though  the  stars 
do  not  look  at  all  as  the  sun  does.  The  sun  looks  large,  and  it 
is  hot,  because  it  is  close  to  us.  The  stars  look  small  because 
they  are  so  far  off,  and  we  get  no  heat  at  all  from  them,  though 
we  get  light.  You  know  you  can  see  the  light  of  a  lamp  much 
farther  than  you  can  feel  its  heat. 

Number  of  the  Stars.  —  Agnes.  There  are  thousands  and  thou- 
sands of  stars,  Jack ;  do  you  know  how  many  there  are  ? 

Jack.  There  are  about  6000  stars  that  you  can  see  with  the 
naked  eye,  not  more;  and  you  cannot  see  all  those  at  once. 
Probably  you  never  see  more  than  a  couple  of  thousands  at  any 
one  time. 

Agnes.    Why,  there  seem  to  be  many  more  than  2000. 


ASTRONOMY 


39 


Jack.  Well,  my  dear,  the  only  way  to  know  is  to  count  them. 
And  the  astronomers  have  counted  them,  and  made  maps  that 
show  every  one  of  them  by  a  little  dot.  That  is  the  way  they 
know  how  many  there  are.  But  if  you  take  an  opera  glass,  you 
can  see  very  many  more ;  and 
if  you  take  a  telescope,  you  can 
see  thousands  and  thousands. 
The  largest  telescopes  that  we 
have  will  show  perhaps  a  hun- 
dred million  stars.  The  bright- 
est stars  are  nearest  to  us,  and 
the  faint  ones  are  very  far  away 
indeed  —  inconceivably  far,  in 
fact. 

Tom.  You  said  the  nearest 
star  was  as  far  away  from  the 
sun  on  our  map  as  New  York 
is  from  Peking.  Are  all  the 
stars  as  far  apart  as  that  ? 
Are  n't  some  of  them  close 
together  ? 

Clusters  of  Stars. — Jack. 
Well,  there  are  some  groups  of 
stars  fairly  close  together;  but 
generally  one  star  is  about  as 
far  from  the  star  nearest  to  it 
as  our  sun  is  from  the  nearest 
star.  If  you  were  making  a  map  of  the  whole  universe,  you 
would  begin  by  making  a  model  of  the  solar  system  just  as  you 
did  yesterday.  The  library  globe  would  stand  for  the  sun, 
which  is  one  of  the  stars,  you  know.  The  nearest  star  to  it 


FIG.  27.     THE  GROUP  OF  STARS 
CALLED  THE  PLEIADES 

The  six  brightest  stars  can  be  seen  with 
the  naked  eye.  To  see  the  others  a  small 
telescope  must  be  used.  The  Pleiades 
may  be  seen  high  up  in  the  sky  and  to 
the  south  of  the  point  overhead  about 
10  P.M.  December  21,  about  9  P.M. 
January  5,  about  8  P.M.  January  20, 
every  year.  Or  you  may  see  them  rising 
to  the  north  of  the  east  point  of  your 
horizon  about  10  P.M.  August  23,  about 
9  P.M.  September  8,  about  8  P.M.  Sep- 
tember 23. 


40  THE    SCIENCES 

would  be  shown  on  the  map  by  a  globe  set  down  at  Peking, 
8000  miles  away  from  us,  and  8000  miles  from  Peking  there 
would  be  another  globe,  and  8000  miles  farther  another  one, 
and  so  on.  Every  8000  miles  on  your  map  there  would  be  a 
globe  to  stand  for  a  star,  and  there  would  be  at  least  a  hundred 
million  globes  on  your  map  of  the  universe,  because,  you 
know,  the  telescopes  show  us  at  least  a  hundred  million  stars. 
Of  course  these  stars  are  scattered  all  around  us  ;  they  are  n't 


«? 

Sun 


ft  $  *  ft  0  $  & 

FIG.  28 

The  stars  in  space  are  arranged  somewhat  as  in  the  picture.  On  the  whole,  no  one  of  them 
is  nearer  to  any  other  one  than  the  sun  is  to  the  nearest  star,  —  20,000,000,000,000  miles. 
The  Sun  is  just  one  out  of  a  countless  number  of  stars  —  one  out  of  millions.  No  one 
of  the  planets  of  the  solar  system  can  be  seen  from  the  nearest  of  the  stars. 

in  a  straight  line  one  after  another,  but  they  are  scattered  all 
over  the  surface  of  the  night  sky. 

Agnes.  The  planets  move  around  the  sun ;  do  the  stars 
move  around  the  sun,  too  ? 

Jack.  No,  they  are  so  far  off  from  us  that  the  sun  has 
nothing  to  do  with  them,  nor  they  with  the  sun.  The  sun  has 
its  own  family  of  planets,  and  it  is  possible  that  the  stars  — 
which  are  suns  —  have  their  own  planets,  too  ;  but  we  do  not 
know  whether  they  have  or  not. 


ASTRONOMY 


Agnes.    Why  don't  you  know,  Jack  ? 

Jack.  Because  the  stars  are  so  far  away.  We  can  see  the 
stars  like  bright  shining  points  in  the  sky.  They  shine  by 
their  own  light  and  are  bright.  Now  suppose  any  one  of  the 
stars  really  had  a  family  of  planets  around  it.  Those  planets 


FIG.  29 

A  photograph  of  a  part  of  the  Milky  Way.  Each  little  dot  in  the  picture  is  a  star,  and  there 
are  thousands  of  them  even  on  one  photographic  plate.  You  can  see  the  Milky  Way  like 
a  bright  belt  in  the  sky  —  a  beH  made  of  stars  —  overhead  early  in  the  evenings  of 
August  and  September  or  of  November,  December,  and  January,  or  parallel  to  the 
northern  horizon  early  in  the  evenings  of  April  and  May. 

would  shine  by  the  light  from  that  star,  and  they  would  be 
faint,  much  too  faint  for  us  to  see,  even  if  the  planets  were 
really  there  ;  and  the  only  way  to  know  about  stars  and 
planets  is  to  see  them  ;  you  cannot  touch  them  or  hear  them. 
If  you  cannot  see  a  planet  it  does  not  exist,  so  far  as  you  know. 


42  THE  SCIENCES 

Tom.  Could  n't  a  man  on  the  nearest  star,  looking  at  our 
sun,  see  the  planets  of  our  system,  —  Venus  and  Jupiter  ? 

Jack.  No,  indeed  ;  he  would  see  our  sun,  but  the  light  of  our 
planets  would  be  too  faint.  He  could  not  possibly  see  them. 

Do  the  Stars  have  Planets  as  the  Sun  does  ?  —  Tom.  You 
say  you  don't  know  whether  the  stars  have  planets  round 
them.  What  do  you  think  about  it  ?  Haven't  you  any  idea? 


•  - 

FIG.  30.     THE  STARLIT  SKY 

Jack.  There  is  a  great  deal  of  difference  between  knowing 
and  thinking.  I  certainly  do  not  know  that  the  stars  have 
planets,  for  I  have  never  seen  them.  But  I  do  think  that  it  is 
very  likely  that  they  have  families  of  planets,  just  as  the  sun 
has.  I  think  it  is  likely  —  very  likely  ;  but  I  don't  know. 


ASTRONOMY 


43 


Tom.    And  do  you  think  those  planets,   if  there   are   any, 
have  people  on  them  ?     Are  they  inhabited  as  the  earth  is  ? 

Jack.  That  is  a  hard  question.  In  the  first  place,  it  is  not 
certain  that  there  are  any  planets  around  the  stars,  and  then  it  is 
a  mere  guess  whether  there  could  be  inhabitants  on  them.  That 
is  one  of  the  questions  we  shall  have  to  give  up.  It  is  too  difficult. 


FIG.  31.     THE  SHOWER  OF  SHOOTING  STARS  SEEN  ON  Nov.  13,  1866 

The  round  dots  stand  for  stars ;  the   arrows  for  the  tracks   of   meteors  that  were  seen. 
Notice  that  nearly  all  the  meteors  radiated  from  a  spot  near  the  center  of  the  picture. 

Agnes.  I  am  going  to  believe  that  every  star  has  planets 
round  it,  just  as  the  sun  has. 

Jack.  Well,  that  is  reasonable  enough.  Very  likely  you  are 
right.  Who  knows  ? 

Agnes.  And  I  am  going  to  believe  that  some  of  these 
planets  round  the  stars  have  men  on  them. 


44 


THE  SCIENCES 


Jack.  I  can't  say  you're  wrong  ;  I  can't  prove  that  you  are 
wrong.  Who  knows  ?  You  can  believe  what  you  like  about 
it.  Wait  till  we  know  more. 

Shooting  Stars ;  Meteors ;  Fireballs.  —  On  the  night  of 
August  10  the  children  stayed  up  late  to  watch  the  shooting 


FIG.  32.    THE  GREAT  METEOR  THAT  FELL  IN  CALIFORNIA  IN  1894 

stars  that  are    regularly  seen    every  year  on   that   particular 
night.     On  almost  any  night  that  is  clear  any  one  who  will 


ASTRONOMY 


45 


watch  for  an  hour  will  see  a  dozen  or  more  ;  and  the  easiest 
way  to  understand  what  they  are  like  is  to  watch  for  them.  In 
the  country,  where  the  sky  is  dark  and  where  there  are  no 
electric  lights,  it  is  not  hard  to  see  them.  In  the  city  it  is 
not  so  simple ;  the  sky  is  too 
bright  and  the  street  lamps 
interfere  too  much.  Any  one 
can  see  the  stars.  If  one  of 
the  stars  should  suddenly  get 
brighter  and  move  quickly 
away  from  its  place  and  then 
suddenly  disappear,  as  if  it 
had  been  blown  out  like  a 
candle,  it  would  look  just  as 
the  shooting  stars  do.  The 
real  stars  stay  in  the  same 
place  night  after  night,  year 
after  year,  century  after  cen- 
tury. They  are  called  fixed 
stars  because  they  are  fixed 
in  their  places.  The  shoot- 
ing stars  are  small  pieces  of 
stone  or  iron  that  are  mov- 
ing about  in  space,  as  the 
planets  move.  One  of  these 
pieces  comes  near  to  the 

earth  and  falls  to  the  ground  just  as  a  stone  falls.  It  moves 
rapidly  through  the  air  and  gets  hot,  as  your  hand  will  get  hot 
if  you  move  it  very  rapidly  to  and  fro  on  your  desk.  The 
shooting  star  moves  very  fast  and  gets  very  hot  indeed  —  hot 
enough  to  burn.  Usually  the  meteors  (shooting  stars)  get  so 


FIG.  33.     A  METEORIC  STONE  THAT 

FELL    IN    IOWA    IN    1875 


46  THE  SCIENCES 

hot  in  their  flight  through  the  air  that  they  are  quite  burned 
up  before  they  reach  the  ground.  Sometimes  a  piece  of  iron 
falls  and  is  picked  up.  The  picture  shows  a  piece  of  the 
sort.  Fig.  32  shows  how  such  a  meteor  (a  very  large  one 
—  much  larger  than  a  shooting  star)  looks  as  it  is  falling. 


FIG.  34.     THE  ZODIACAL  LIGHT 

The  best  time  to  see  it  in  the  United  States  is  in  February,  March,  and  April,  in  the  early 
evening,  above  the  western  horizon. 

The  Zodiacal l  Light.  —  Space  is  full  of  such  meteors,  most 
of  them  small,  like  dust.  The  sun  shines  on  them,  and  you 
can  often  see  a  triangle  of  faint  light  or  glow,  which  is  called 

1  Pronounced  zo-di'a-kal. 


OF  THE 


OF 


ASTRONOMY 


47 


the  zodiacal  light.  If  you  live  in  the  country,  where  the  sky 
is  dark,  be  on  the  lookout  for  it.  The  street  lamps  of  the  city 
make  the  sky  entirely  too  bright  for  you  to  see  it  in  towns. 
Nebulae.  —  Nebula,  in  Latin,  means  a  cloud ;  and  nebulae  is  the 
plural.  There  are  several  spots  in  the  sky  that,  even  with  the 


FIG.  35.     THE  GREAT  NEBULA  IN  ANDROMEDA,  FROM  A  PHOTOGRAPH 

MADE   WITH   A    TELESCOPE  (SEE  FlG.   53) 

naked  eye,  on  a  clear  night  look  as  if  the  stars  in  those  spots  were 
covered  with  a  thin  veil  of  cloud.  When  these  spots  are  looked 
at  with  a  telescope  you  see  bright  forms  like  those  in  the  pictures 
Figures  35  and  53,  and  they  are,  in  fact,  bright  clouds  of  gas 
and  small  particles  of  dust.  They  shine  by  their  own  light. 


48 


THE  SCIENCES 


Rising  and  Setting  of  the  Sun.  —  Tom.  We  know  that  the 
sun  rises  in  the  east  every  day  — 

Agnes.    And  goes  across  the  sky  and  sets  in  the  west. 

Jack.    Why  does  it  ?     Does  the  sun  really  move  ? 

Agnes.  No ;  the  earth  turns  round  and  the  sun  stands  still ; 
but  the  sun  seems  to  move. 

Jack.  The  sun  seems  to  move  across  the  sky  from  rising  to 
setting  every  day ;  the  moon  does  the  same  thing  ;  each  one  of 
the  thousands  of  stars  rises  and  then  sets  every  night.  There 
are  just  two  ways  to  explain  these  things.  Either  the  earth 
stands  still  and  all  these  different  heavenly  bodies  really  move 
around  it  —  every  one  of  them  —  in  twenty-four  hours,  or  the 


FIG.  36.     THE  SETTING  SUN 

heavenly  bodies  stand  still  and  the  earth  turns  round  on  its 
axis  every  day.  The  last  explanation  is  the  true  one,  as  you  know 
very  well,  and  so  we  have  to  say  the  sun  appears  to  move  from 


ASTRONOMY 


49 


rising  to  setting  (for  the  sun  really  does  not  move  at  all) ;  and 
we  have  to  say  the  stars  appear  to  move  from  rising  to  setting 
(for  the  stars  do  not  really  move  at  all).  It  is  the  earth  that 


FIG.  37.     THE  WAY  THE  SUN  SEEMS  TO  MOVE  FROM  RISING  TO  SETTING 

The  man  in  the  picture  is  looking  towards  the  south,  and  his  arms  are  stretched  out  to  the  east 
and  to  the  west.  If  he  stood  there  all  day,  he  would  see  the  sun  rise  above  the  horizon 
in  the  east,  gradually  rise  higher  and  higher  and  be  highest  at  noon,  just  to  the  south, 
and  then  decline  towards  the  west  and  set  in  the  west  at  the  end  of  the  day.  The 
dotted  line  shows  the  apparent  motion  of  the  sun.  The  picture  was  drawn  at  about 
three  o'clock  in  the  afternoon.  Why  ?  Because  the  sun  in  the  picture  is  where  the 
real  sun  will  be  every  day  about  three  o'clock. 

turns,  and  as  it  turns  everything  in  the  sky  appears  to  move 
from  east  to  west. 

The  Celestial  Sphere.  —  "  Think  of  it  in  this  way.  You  are 
on  a  globe  —  the  earth  —  that  turns  around  every  twenty-four 
hours.  Above  you  is  the  sky.  It  looks  exactly  as  if  it  were 
a  hollow  globe,  and  as  if  you  were  inside  of  it.  In  the  night- 
time the  stars  look  like  little  shining  marks  fastened  to  the 
hollow  globe  all  around  you.  In  the  daytime  the  sun  (and 
sometimes  the  moon)  seems  to  be  fastened  to  the  inside  of  the 
hollow  globe  of  the  sky.  We  call  the  hollow  globe  of  the  sky 


50  THE  SCIENCES 

the  celestial  sphere.  You  are  in  the  middle  of  it,  and  you  see 
all  the  stars  at  night  slowly  moving  from  rising  towards  setting. 
The  celestial  sphere  is  the  surface  of  the  sky  to  which  the  sun, 
moon,  and  stars  appear  to  be  fastened.  They  look  as  if  they  were 
fastened  there,  anyway.  They  all  seem  to  be  at  the  same  distance." 


FIG.  38.     THE  CELESTIAL  SPHERE  (THE  HOLLOW  GLOBE  ON  WHOSE 
INNER  SURFACE  ALL  STARS  SEEM  TO  LIE) 

The  earth  is  supposed  to  be  at  O,  and  some  stars  at  /,  <?,  r,  s,  /,  t,  /,  u,  v.  You  see  the  stars 
as  if  they  were  all  projected  on  the  celestial  sphere  at  P,  Q,  If,  S,  T,  U,  V.  You  think 
of  them  as  if  they  were  all  at  the  same  distance  from  you. 

Tom.  They  can't  all  be  fastened  to  any  one  sphere,  because 
they  are  at  very  different  distances  from  us.  The  sun  .is  very 
much  further  away  from  us  than  the  moon,  and  the  stars  are 
much  further  off  than  the  sun. 


ASTRONOMY 


Jack.  True  enough.  If  you  will  look  at  this  picture  I  am 
drawing,  you  will  see  how  it  is.  You  are  supposed  to  be  in  the 
middle  of  the  celestial  sphere  at  O.  The  earth  is  at  O  (Fig.  38), 


FIG.  39 

This  picture  shows  the  northern  sky  as  it  appears  in  the  early  hours  of  the  evening  every 
August  to  people  who  live  in  the  United  States.  If  you  face  north,  you  see  the 
horizon  *  —  the  surface  of  the  ground.  Above  that  comes  the  sky  with  many  stars  in 
it.  Towards  the  west  and  pretty  high  up  is  the  Dipper  —  the  Great  Bear  (Ursa 
Major).  Two  of  its  stars  —  the  pointers — point  at  the  north  star — Polaris,2  it  is 
called.  High  in  the  east  is  Cassiopeia,3  a  group  that  is  sometimes  called  The  Lady  in 
the  Chair.  Every  child  that  owns  this  book  should  try  to  find  these  stars.  They  are 
always  there,  in  the  north.  If  he  looks  in  August  they  will  be  just  as  in  the  picture. 
If  he  looks  in  other  months  the  book  must  be  turned  a  little.  By  taking  a  little  pains 
the  book  can  be  held  so  that  the  picture  will  look  as  the  stars  do. 

1  Pronounced  ho-ri'zon.   2  Pronounced  po-la'ris.    3  Pronounced  kas"i-o-pe'ya. 


52  THE  SCIENCES 

and  you  are  on  it.  All  around  you  are  stars,  /,  q,  r,  s,  etc. 
You  see  the  star  q  along  the  line  Oq  —  along  the  line  that 
joins  your  eye  and  the  star.  The  line  seems  to  pierce  the 
celestial  sphere  at  Q,  and  you  think  the  star  q  is  really  at  Q. 
In  the  same  way  you  think  the  star  r  is  at  R,  the  star  s  at  S, 
and  so  forth.  If  there  were  really  three  stars,  t,  /,  /,  all  in  one 
line,  Ot,  you  would  see  only  one  star  at  T.  All  the  stars  seem 
to  be  lying  on  the  surface  of  some  sphere,  and  all  of  them  seem 
equally  far  away. 

Tom.  That  is  true,  I  know.  When  I  look  at  the  stars  at 
night  they  certainly  do  seem  to  be  all  at  one  distance  —  just 
like  shining  tacks  driven  into  a  darkish  globe  above  my  head 
and  all  around  me. 

Agnes.  And  in  the  daytime  the  sun  and,  sometimes,  the 
moon  seem  to  be  the  same  way  —  shining  circles  fastened  on 
to  a  shining  globe. 

Jack.  Of  course  there  is  n't  any  real  globe  there.  It  is  only 
an  appearance.  But  it  looks  real,  and  we  have  a  name  for 
the  appearance  because  it  is  convenient  to  have  names  for 
things  we  always  see,  or  even  for  things  that  we  always 
think  that  we  see. 

Tom.  You  would  have  a  model  of  the  celestial  sphere  by 
making  a  huge  hollow  globe  as  big  as  a  barn  and  getting  inside 
of  it. 

Agnes.  Yes,  and  by  lining  it  with  black  velvet  and  driving 
bright-headed  tacks  into  the  lining  for  stars  ;  only  you  would 
have  to  drive  them  in  the  right  places. 

Jack.  A  model  like  that  would  be  worth  making,  but  it 
would  be  expensive.  We  shall  have  to  do  with  pictures 
and  flat  maps.  They  will  explain  what  we  really  see  in 
the  sky. 


ASTRONOMY 


53 


The  next  night  Jack  took  the  children  out  of  doors.  He  made 
them  face  towards  the  north  ;  the  east  was  on  their  right  hand, 
the  west  on  their  left.  First  of  all  he  showed  them  the  Dipper 
—  the  Great  Bear  (Ursa  Major  in  Latin)  —  and  the  pointers. 

The  Dipper  is  made  up  of  seven  bright  stars  and  is  always 
easy  to  find.  Three  of  its  stars  make  the  handle,  four  make 

the  bowl,  and  two  stars  of    ,gg^_—  

the  bowl  are  the  pointers. 
After  you  have  found  the 
pointers  it  is  easy  to  find 
the  polestar.  Now  if  you 
imagine  a  line  drawn  from 
the  polestar  to  the  center 
of  the  earth  (under  your 
feet),  that  line  will  be  the 
axis  of  the  earth.  The 
earth  turns  round  that 
line  every  day.  Every 
part  of  the  axis  itself 
stands  still,  and  every 
point  not  in  the  axis 
moves.  The  center  of  the 
earth  stands  still  while 
the  earth  turns ;  and  Pola- 
ris stands  still.  All  the 
parts  of  the  earth  not  on  the  axis  appear  to  move,  and  all  the 
stars  except  Polaris  appear  to  move  —  they  move  from  rising 
to  setting  and  back  to  rising  again.  The  stars  in  the  east 
move  upwards,  then  over  the  pole  towards  the  west,  and 
then  downwards  (in  the  direction  of  the  little  arrows  in 
Figs.  39  and  40). 


FIG.  40.    THE  DIPPER  —  THE  GREAT  BEAR  — 
AS  IT  APPEARS  AT  DIFFERENT  TlMES 

Sometimes  it  is  above  the  pole,  sometimes  below  it; 
but  if  you  lay  a  ruler  on  the  picture,  you  will  see 
that  the  pointers  always  point  to  the  north  star  — 
Polaris. 


54  THE  SCIENCES 

Jack  kept  the  children  out  of  doors  till  long  after  their  bed- 
time to  let  them  see  the  stars  rise  higher  and  higher,  but  finally 
they  had  to  go  to  bed.  They  could  not  watch  any  longer. 

On  the  next  night  Jack  showed  the  children  how  the  southern 
stars  appeared  to  move  from  rising  to  setting.  He  took  them 


FIG.  41 

A  photograph  of  a  part  of  the  northern  sky  near  the  pole.  A  camera  was  pointed  at  the 
pole  early  in  the  evening  and  the  plate  was  exposed  all  night  and  only  shut  off  at  day- 
break. Each  star  moved  about  half  of  its  course  round  the  pole,  and  as  it  moved  it 
left  a  trail  on  the  plate.  All  the  trails  in  the  picture  are  half  circles.  The  star 
Polaris  is  not  exactly  at  the  north  pole  of  the  heavens  (though  it  happens  to  be  pretty 
near  it).  Its  trail  is  the  brightest  one  on  the  plate.  The  other  stars  left  their  trails,  too. 


ASTRONOMY  55 

out  into  a  large  open  field  and  made  them  face  towards  the 
south.  The  east  was  on  their  left  hand,  the  west  on  their 
right  hand,  and  the  stars  appeared  to  move  from  east  to  west, 
—  from  rising  towards  setting  —  just  as  the  sun  does.  The 


FIG.  42 

A  photograph  of  a  part  of  the  southern  sky,  showing  the  trails  of  southern  stars  as  they 
moved  across  the  plate  from  rising  towards  setting.  This  photograph,  and  the  one  like 
it  for  the  northern  stars,  prove  that  the  stars  really  move  with  respect  to  the  photo- 
graphic plate.  But  it  is  not  the  stars  that  move.  The  plate  moves  with  the  earth  as 
the  earth  turns  round  its  axis.  The  stars  stand  still. 

apparent  motion  of  all  the  stars  —  of  the  south  stars  as  well  as 
of  the  north  stars —  is  caused  by  one  thing  and  one  thing  only. 
The  earth  turns  round  on  its  axis  underneath  the  starry  sky. 


56  THE  SCIENCES 

Time  and  Timekeeping.  —  We  use  the  apparent  motion  of  the 
sun  from  rising  to  setting  to  give  us  the  time.  Watches  and 
clocks  all  over  the  world  are  now  regulated  by  the  sun.  Long 
ago  the  ancients  used  to  tell  their  time  by  the  stars.  They 
would  say:  "You  must  begin  your  journey  when  the  Pleiades 
are  rising";  just  as  we  might  say:  "I  must  take  the  train  at 
9  P.M."  Groups  of  stars,  like  the  Pleiades,  were  the  moving 
clock  hands  ;  the  dial  was  the  celestial  sphere.  The  stars  moved 
steadily  across  the  dial,  and  their  motion  told  the  hour.  The 
sun  moves  regularly  and  steadily  from  rising  to  setting.  When 
it  is  highest  up  in  the  heavens  and  exactly  south  of  any  place 
(a  city,  a  town,  any  place),  then  it  is  noon  at  that  particular 
place.  Twelve  hours  later  it  is  midnight ;  and  twelve  hours 
later  than  midnight  it  is  noon  again  —  noon  of  the  next  day  of 
the  week.  A  watch  is  a  little  machine  arranged  to  drive  a 
steel  hand  round  a  dial  in  twelve  hours.  The  hand  is  set  so  as 
to  mark  XII  o'clock  at  noon,  and  the  machine  is  regulated  so 
that  when  the  next  noon  comes  the  hand  shall  be  at  XII  again. 
To  set  our  watches  exactly,  we  must  have  a  north  and  south 
line.  Astronomers  have  a  particular  kind  of  telescope  set 
exactly  in  the  north  and  south  line  (the  meridian),  so  that  they 
can  observe  the  exact  instant  of  noon.  Their  watches  are 
corrected  so  as  to  mark  XII  o'clock  just  at  that  moment;  and 
made  to  run  so  that  when  the  next  noon  comes  they  will  mark 
XII  o'clock  again.  They  have  other  kinds  of  telescopes  also, 
especially  made  to  examine  distant  planets  and  to  discover 
what  is  to  be  seen  on  their  surfaces. 

Telescopes.  —  The  children  were  playing  with  a  reading  glass 
that  belonged  to  their  father.  Tom  used  it  to  light  a  match 
with,  and  then  to  look  at  the  wings  of  a  fly,  and  noticed  how 
it  magnified  everything  —  how  it  made  it  look  much  larger. 


ASTRONOMY 


57 


Then   he   said  :   "Jack,   what   is   the   difference  between   this 

magnifying  glass  and  a  telescope  ?     Both  of  them  magnify." 

Jack.    Well,  the  telescope  magnifies  very  much  more,  for  one 


FIG.  43.     A  MERIDIAN  CIRCLE 

The  eye  end  of  the  telescope  is  at  M.  The  telescope  is  fastened  to  a  horizontal  axis  which 
lies  in  an  east  and  west  line,  and  the  telescope  always  remains,  therefore,  in  the  meridian. 
LL  is  a  level  by  which  the  axis  is  made  horizontal.  The  axis  has  two  circles  (Hand  K) 
fastened  to  it.  These  circles  are  divided  into  360  degrees,  and  by  them  we  can  measure 
the  altitude  (height)  of  any  star. 


58  THE  SCIENCES 

thing  ;    and  a  telescope  is  made  up  of  more  than   one  lens. 
The  burning  glass  has  only  one. 

Jack  took  the  burning  glass  and  showed  the  children  how  to 
use  it  to  make  an  image  (a  picture)  of  the  window  on  the  wall, 
as  in  Fig.  45. 

Jack.   You  see  that  this  glass  makes  an  image  of  the  window 
on  the  wall.     Suppose  that  we  should  cut  a  hole  in  the  wall 
just  where  the  image  is  now.     The  image 
would  be  there  just  the  same,   for  if  you 
put  a  piece  of  white  paper  over  the  hole 
the  image  would  show  on  the  paper  as  it 
now  does  on  the  wall.     Now  suppose  that 
you   were   in   the   other  room   beyond  the 
wall    and    held    another    burning  glass   in 
just  the  right  place  to  magnify  the  image 
in  the  hole.      The    second    burning   glass 
magnifies  everything  it  looks  at  ;  well,  you 
could  use  it  to  magnify  the  image  formed 
by  the  first  burning  glass.     If  you  did  this, 
you  would  have  a  telescope.     Two   lenses 
FIG.  44.    A  READING   combined  so  as  to  form  a  magnified  image 
GLASS,  A  MAGNIFY-   of  anv  object  make  a  telescope.     One  lens 
ING  LENS,  OR  A      .  .  ,  . 

BURNING  GLASS        alone  ls  not  a  telescope  ;    it  is  a  magnify- 
ing glass. 

Agnes.  Then  a  telescope  must  have  two  glasses  ? 
Jack.  Yes,  two  at  least ;  the  first  glass  forms  an  image  of 
the  thing  you  are  looking  at  —  a  picture  of  the  window,  for 
instance.  The  second  glass  magnifies  the  image  so  that  you 
can  see  it  better  and  see  it  larger.  All  opera  glasses  and 
spyglasses  have  at  least  two  lenses,  usually  more  than 
two. 


ASTRONOMY  59 

Tom.    Here  is  a  drawing  of  the  great  telescope  of  the  Lick 
Observatory  (Fig.  46).     Where  are  the  two  glasses  there  ? 

Jack.    One  of  them  is  at  the   upper  end  of  the  long  steel 
tube  ;  they  call  it  the  object  glass,  because  it  is  nearest  the 


FIG.  45 

If  you  hold  a  burning  glass  in  a  room,  you  can  make  it  form  an  image  (a  picture)  of  the 
window  on  the  opposite  wall.  The  image  will  be  clear  and  distinct,  but  it  will  be  upside 
down,  as  you  can  prove  by  trying.  Most  lenses  will  need  to  be  held  nearer  the  wall 
than  that  in  the  figure. 

object  you  are  looking  at.  The  other  glass  is  at  the  other  end 
of  the  tube  ;  they  call  it  the  eyepiece,  because  it  is  next  your  eye. 
In  the  drawing  you  see  a  man  looking  through  the  eyepiece. 

Agnes.    But  the  telescope  is  inside  a  house,  Jack.     How  can 
the  astronomer  see  anything  ? 


60  THE  SCIENCES 

Tom.  Why,  you  know,  Agnes,  that  there  is  a  long  window 
in  the  dome  that  is  opened  when  they  want  to  look  out  to  see 
anything.  The  telescope  looks  out  through  the  open  window. 

Agnes.    What  is  the  long  tube  for  ? 

Jack.  It  is  principally  to  keep  the  object  glass  and  the  eye- 
piece at  exactly  the  right  distance  apart  and  to  hold  them 
steadily  where  you  want  them. 

Tom.  The  tube  is  on  an  iron  stand,  and  you  can  go  to  the 
top  of  the  stand  by  a  winding  stairway.  What  are  those  big 
circles  at  the  top,  Jack  ? 

Jack.  The  circles  are  fastened  to  the  telescope,  Tom,  not  to 
the  iron  stand,  you  see  ;  and  they  are  arranged  to  show  the 
latitude  and  the  longitude  of  the  particular  star  that  the  tele- 
scope is  pointed  at. 

Agnes.    Do  they  know  the  latitudes  and  longitudes  of  stars  ? 

Jack.  Yes,  that  is  the  way  they  point  at  them.  If  I  tell  you 
to  find  on  the  map  a  town  that  has  a  latitude  of  41°  and  a 
longitude  of  80°,  you  can  find  it,  can't  you  ? 

Agnes.    Here  is  the  map,  and  the  town  is  Pittsburg. 

Jack.  Well,  the  astronomers  have  maps  of  the  stars,  and 
they  find  the  star  they  want  by  knowing  its  latitude  and 
longitude,  and  by  pointing  the  telescope  there. 

Tom.  But  the  star  would  be  moving  from  rising  to  setting. 
How  do  they  manage  to  follow  it  ? 

Jack.  If  you  will  look  at  the  drawing  of  the  telescope 
(Fig.  46),  you  '11  see  a  piece  of  machinery  in  the  top  part  of  the 
stand.  It  is  really  a  powerful  clock.  That  clock  is  arranged 
so  as  to  move  the  telescope  towards  the  west  exactly  as  fast  as 
the  star  moves  toward  the  west.  When  you  once  have  the  star 
in  the  telescope  the  clock  keeps  it  there. 

Agnes.    How  large  is  the  object  glass  of  the  Lick  telescope? 


FIG.  46.    THE  GREAT  TELESCOPE  OF  THE  LICK  OBSERVATORY 

Its  object  glass  is  three  feet  in  diameter,  and  it  is  nearly  sixty  feet  long. 

61 


62 


THE    SCIENCES 


Jack.    The  object  glass  is  three  feet  in  diameter,  and  the  tube 

is  nearly  sixty  feet  long,  and  the  eyepiece  is  quite  small  —  just 

the  size  to  be  convenient  for  your  eye  to  see  through,  Agnes. 

Tom.    How  much  can  you  magnify  with  a  telescope  like  that  ? 

The  Moon.  — Jack.    Well,  you  can  arrange  so  as  to  magnify 

more  or  less  as  you  please.     For  instance,  you  can  magnify 

the  moon  about  a  thou- 
sand times  —  you  can  see 
the  moon  as  if  it  were 
a  thousand  times  nearer 
than  it  really  is.  How 
far  off  did  I  tell  you  the 
moon  is  ? 

Tom.  Two  hundred 
and  forty  thousand  miles. 
Jack.  Then  if  the  tele- 
scope will  make  it  seem 
a  thousand  times  nearer, 
how  far  off  will  it  seem 
to  be  ? 

Agnes.    Two    hundred 
and  forty  miles. 

Jack.  That 's  right,  my 
dear.  The  Lick  telescope 
will  show  you  the  moon 
just  as  you  would  see  it  if  you  got  within  two  hundred  and 
forty  mi?es  of  it  —  just  as  if  the  moon  were  at  Pittsburg  and 
you  at  Philadelphia. 

Agnes.    That  does  not  seem  to  be  very  near. 
Jack.    Well,  it  is  n't  near ;  but  it  is  wonderful  to  do  even  so 
well  as  that. 


FIG.  47.     MOUNTAINS  ON  THE  MOON, 
AS  SEEN  IN  A  TELESCOPE 


ASTRONOMY 


Tom.    Then  the  planets,  that  are  so  much  farther  away  than 
the  moon,  cannot  be  seen  anything  like  so  well  ? 

Jack.  No ;  Mars,  for  instance,  is  50,000,000  miles  away 
from  us  when  we  see  it  best,  and  so  we  never  can  make  it 
seem  nearer  to  us  than  50,000  miles.  That  is  better  than 
nothing ;  but  it  is  n't  very  close,  after  all.  It  is  really  wonder- 
ful that  men  have  found 
out  so  much  as  they  have 
about  the  planets  when 
you  consider  what  the 
difficulties  are.  The 
smallest  spot  that  can  be 
seen  with  distinctness  on 
the  moon  would  contain 
several  acres ;  and  when 
you  come  to  looking  at 
a  distant  planet  like  Mars 
a  spot  would  have  to  be 
fifty  or  sixty  miles  square 
to  be  visible  at  all. 

Tom.    Then  you  might 
see  a  city  on  the  moon? 

A  city  covers  many  acres. 

r    .      _r  FIG.  48.     MOUNTAINS  ON  THE  MOON, 

Jack.    You  could  see  a  AS  SEEN  IN  A  TELESCOPE 

city    on    the  moon   if    it 

were  there;  or  even  a  very  large  building  like  the  Capitol  at 
Washington ;  but  there  are  no  such  cities  or  buildings  on  the 
moon.  Astronomers  have  looked  for  them  thousands  of  times 
without  ever  finding  the  slightest  sign  of  any  living  thing. 

Life  on  the  Planets.  —  Agnes.    Is  there  any  sign  of  life  on 
the  planets  ? 


64  THE  SCIENCES 

Jack.  Not  one;  life  of  some  sort  may  be  there  —  plants, 
trees,  animals,  or  possibly  men  —  but  the  telescope  shows  no 
sign  of  life  at  all. 

Tom.    Not  even  on  Mars  ? 

Jack.  Not  even  on  Mars  —  nowhere.  Some  people  have 
talked  about  land  and  water  on  Mars,  calling  parts  of  Mars 
that  are  reddish,  land,  and  parts  that  are  bluish,  water ;  but 
no  one  has  any  proof  at  all  that  the  red  parts  are  really  land, 
or  the  blue  parts  water. 

Tom.    I  have  read  about  canals  in  Mars. 

Jack.  Well,  whatever  they  are,  they  are  not  canals.  The 
telescope  shows  narrow,  straight,  dark  lines  on  the  planet's 
surface  (see  Fig.  49),  and  they  were  called  canals  because  they 
crossed  the  red  parts  of  Mars  that  were  called  continents.  But 
the  Lick  telescope  shows  that  the  canals  go  across  the  oceans, 
just  as  they  go  across  the  continents ;  so  that  it  is  pretty 
clear  that  the  canals  are  not  canals  at  all,  and  that  we  do  not 
know  whether  Mars  has  any  water  on  its  surface  at  all. 
Tom.  How  is  it  about  Jupiter  ? 

Jack.  Jupiter  looks  as  if  it  were  a  very  hot  planet ;  like  a  huge 
red-hot  ball  covered  with  clouds  of  steam.  All  of  Saturn  that  we 
can  see  seems  to  be  clouds  ;  and  the  same  is  true  for  Uranus  and 
Neptune,  and  for  Venus,  too,  for  that  matter.  Mercury  and 
Mars  have  no  clouds  and  probably  little  or  no  atmosphere  at  all. 
All  the  others  have  atmospheres,  but  no  one  knows  whether  their 
air  is  the  right  kind  of  air  to  breathe.  It  is  very  doubtful  whether 
any  planet  beside  the  earth  is  fit  for  men  to  live  on. 
Tom.  Is  there  air  on  the  moon  ? 

Jack.  There  is  no  air  on  the  moon  at  all,  nor  any  water 
either;  and  it  is  so  cold  on  the  moon,  and  on  Mars  too,  that 
no  man  could  possibly  live  there  for  an  instant. 


ASTRONOMY  65 

Tom.    Then  there  is  n't  any  place  in  the  whole  universe  where 
we  are  really  sure  that  men  can  live  except  just  the  earth  ? 

Jack.  No.  Men  cannot  live  in  the  sun ;  the  sun  is  too  hot. 
Jupiter  is  too  hot,  also.  Mercury  and  Mars  have  little  or  no 
air.  Venus,  Saturn,  Uranus,  and  Neptune  are  covered  with 
clouds,  and  we  do  not  know  what  is  underneath  the  clouds. 
Men  couldn't  live  in  the  stars  ;  they  are  like  the  sun  —  too 
hot.  And  we  do  not  know  whether  the  stars  have  planets 


FIG.  49 

Drawings  showing  two  hemispheres  of  the  planet  Mars.  The  narrow  lines  are  what  have 
been  called  canals.  The  dark  parts  of  the  drawing  should  be  colored  blue  and  most 
of  the  white  parts  reddish  in  order  to  make  it  look  as  Mars  does. 


round  them  or  not ;  very  likely  they  have.  If  they  have,  some 
of  their  planets  may  be  fit  for  men  to  live  on.  Agnes  says  she 
is  going  to  believe  it. 

Agnes.  Yes,  I  am.  It  makes  the  universe  more  interesting 
to  believe  that  there  are  people  like  ourselves  everywhere,  or 
at  least  in  many  places. 

Jack.  Well,  believe  it,  my  dear.  I  half  believe  it  myself ;  but 
there  is  no  way  to  prove  it,  or  to  disprove  it,  for  that  matter. 


APPENDIX 


THE  EARTH  (0) 

THE  earth  is  a  globe  flattened  at  the  poles.  Its  shortest  diameter 
(from  pole  to  pole)  is  7900  miles.  Its  longest  diameter  is  7927  miles.  It 
turns  on  its  axis  once  daily.  It  moves  in  its  orbit  round  the  sun  once  in  a 
year  of  365  days  5  hours  48  minutes  451  seconds.  Its  month  (from  new 
moon  to  new  moon)  is  about  29!  days.  The  earth  is  5^  times  as  heavy 
as  a  globe  of  water  of  the  same  size.  The  sun  weighs  333,000  times  more 
than  the  earth.  The  distance  from  the  earth  to  the  sun  is  93,000,000 
miles. 

THE  MOON  (C) 

The  moon  is  2163  miles  in  diameter.  The  moon  weighs  about  3! 
times  as  much  as  a  globe  of  water  of  the  same  size.  The  earth  weighs 
8 1  times  as  much  as  the  moon.  The  distance  from  the  moon  to  the  earth 
is  240,000  miles. 

ECLIPSES  OF  THE  SUN  AND  MOON 
They  are  explained  in  Book  II  (Physics). 

THE  PLANET  MERCURY  (9) 

Mercury  is  3030  miles  in  diameter.  It  weighs  about  3|-  times  as  much 
as  a. globe  of  water  of  the  same  size.  It  goes  once  round  the  sun  every 
88  days.  It  is  36,000,000  miles  distant  from  the  sun — less  than  T%  of 
the  earth's  distance,  therefore. 

THE  PLANET  VENUS  (9) 

Venus  is  7700  miles  in  diameter  (about  the  size  of  the  earth,  therefore). 
It  weighs  4r%  times  as  much  as  a  globe  of  water  of  the  same  size.  It  goes 

66 


ASTRONOMY  —  APPENDIX 


67 


round  the  sun  once  every  225  days.     It  is  67,200,000  miles  distant  from 
the  sun  —  about  T75  of  the  earth's  distance,  therefore. 

THE  PLANET  MARS 


Mars   is   4230  miles  in  diameter.       It  weighs  4  times  as  much    as    a 
globe  of  water  of  the  same  size.     It  turns  once  on  its  axis  in  24  hours 


FIG.  50 
A  rough  drawing  of  the  full  moon. 

37  minutes  22Tyff  seconds.  It  goes  round  the  sun  once  every  687  days.  It 
is  141,500,000  miles  from  the  sun  —  about  i|  times  the  earth's  distance, 
therefore.  It  has  two  very  small  moons. 


JUPITER 

Jupiter  is  86,500  miles  in  diameter.     It  weighs  only  ly^  times  as  much  as 
a  globe  of  water  of  the  same  size.     It  turns  once  on  its  axis   in  9  hours 


68  THE   SCIENCES 

55  minutes.  It  goes  round  the  sun  once  every  IIT%  years.  It  is  483,- 
300,000  miles  from  the  sun  —  about  5  times  the  earth's  distance,  therefore. 
It  has  five  moons.  One  of  them  is  very  small;  the  others  much  larger  — 
about  the  size  of  our  own  moon,  or  of  the  planet  Mars. 


THE  PLANET  SATURN  (^7) 

Saturn  is  made  up  of  a  globe  with  rings  around  it.  The  diameter  of  its 
globe  is  73,000  miles,  It  weighs  only  T7ff  as  much  as  a  globe  of  water  of  the 
same  size.  The  globe  turns  on  its  axis  every  10  hours  14  minutes  24  seconds. 
It  goes  round  the  sun  once  every  29!  years.  It  is  886,000,000  miles  dis- 
tant from  the  sun  —  about  9^  times  the  earth's  distance,  therefore. 

The  rings  of  Saturn  are  made  up  of  a  swarm  of  countless  little  moons. 
The  rings  are  about  28,000  miles  wide  and  168,000  miles  in  diameter,  and 
only  about  100  miles  thick.  Saturn  has  eight  moons  —  otie  as  large  as 
Mars,  one  about  the  size  of  our  moon,  and  the  rest  smaller. 


THE  PLANET  URANUS  (£) 

Uranus  is  31,900  miles  in  diameter.  It  weighs  only  IT27  as  much  as  a 
globe  of  water  of  the  same  size.  It  goes  round  the  sun  once  in  84  years. 
It  is  1,781,900,000  miles  distant  from  the  sun  —  about  19  times  as  far  as 
the  earth,  therefore.  It  has  four  rather  small  moons. 


THE  PLANET  NEPTUNE 

Neptune  is  34,800  miles  in  diameter.  It  weighs  only  IT\J-  times  as  much 
as  a  globe  of  water  of  the  same  size.  It  goes  round  the  sun  once  in 
165  years.  It  is  2,791,600,000  miles  distant  from  the  sun  —  about  30  times 
the  earth's  distance,  therefore.  It  has  one  moon  about  the  size,  of  our 
own  moon. 

COMETS 

A  few  comets  belong  to  the  family  of  the  sun  and  move  around  him 
as  do  the  planets. 


ASTRONOMY  —  APPENDIX 


69 


THE  FIXED  STARS 

Stars  are  suns,  immensely  distant  from  our  sun  and  from  each  other 
except  when  they  are  grouped  in  clusters.  Light,  which  travels  nearly 
200,000  miles  in  a  second,  takes  4 years  to  come  to  us  from  the  nearest  star. 
The  light  from  Polaris  (the  polestar)  takes  47  years  to  reach  the  earth. 


FIG.  51.    THE  TOTAL  SOLAR  ECLIPSE  OF  1871  IN  INDIA 

The  black  circle  is  the  disk  of  the  moon ;  behind  it  the  sun's  disk  is  hidden.  The  pale 
white  streamers  are  the  sun's  corona,  or  crown.  The  corona  always  surrounds  the  sun, 
but  is  not  visible  every  day  because  the  streamers  are  so  faint.  Notice  close  to  the 
edge  of  the  moon's  disk  a  few  brighter  spots.  These  are  flames  of  hydrogen  —  a  gas 
that  is  glowing  as  if  it  were  white  hot  —  in  the  sun's  atmosphere. 


70  THE   SCIENCES 


NEBULAE 

Nebulae  are  masses  of  gas  at  about  the  same  distance  from  the  sun  as 
the  stars  are.  They  are  of  all  shapes  and  sizes.  Many  of  them  are  spiral 
in  shape  —  corkscrew  shaped.  If,  as  sometimes  happens,  a  star  burns  up 
it  may  turn  into  a  nebula ;  or,  as  sometimes  happens,  a  nebula  may  solidify 
and  become  a  star.  Perhaps  our  sun  and  all  the  planets  were  once  a  huge 
nebula  that  cooled  and  solidified  into  separate  globes. 


FIG.  52. 


A  CLUSTER  OF  STARS  IN  THE  CONSTELLATION  OF 
THE  CENTAUR 

Each  white  dot  represents  a  star. 


FIG.  53 

Drawing  of  a  large  nebula  (in  Andromeda)  as  seen  in  a  telescope.    The  white  dots 

are  stars;  the  shining  white  cloud  is  the  nebula.     (See  also  Fig.  35.) 

71 


OF  THE 

UNIVERSITY 

OF 


BOOK  II 


PHYSICS 

THE  SCIENCE  THAT    EXPLAINS   HEAT,   LIGHT, 
SOUND,    ELECTRICITY,    MAGNETISM 


Solids  and  Liquids.  —  "What  is  the  difference  between  a  solid 
and  a  liquid  ?  "  said  Tom  one  hot  afternoon  when  the  children 
were  all  together  on  the  porch,  fanning  themselves. 

Mary.  You  can  pick  up  a  solid  in  your  fingers,  and  you  can- 
not pick  up  a  liquid  —  that's  one  difference. 

Agnes.  You  mean  you  can  pick  up  a  piece  of  ice,  and  you 
cannot  pick  it  up  when.it  has  melted  into  water? 

Mary.    Of  course  you  can't. 

Fred.  Oh,  yes,  you  can  —  and  with  that  Fred  took  a  lump  of 
sugar  and  put  it  in  a  teaspoon  partly  full  of  water.  The  sugar 
took  up  the  water,  and  Fred  picked  up  the  sugar  and  left  the 
spoon  quite  empty,  saying  :  "  Look  at  that !  I  've  picked  up  a 
liquid  in  my  ringers.  It 's  magic." 

Agnes.    That  is  just  foolish,  Fred. 

Fred.  I  know  it  —  but  it  is  magic.  You  said  I  could  n't 
do  it. 

Tom.  It  is  n't  fair,  Fred ;  you  can  pick  up  a  sponge  with 
water  in  it,  but  you  cannot  pick  the  water  up  without  the 
sponge,  nor  the  water  without  the  sugar,  either. 

73 


74 


THE  SCIENCES 


Fred.  All  right.  I  was  just  playing.  It  is  a  kind  of  magic, 
though. 

Mary.  Well,  was  n't  I  right  ?  A  solid  is  a  thing  you  can 
pick  up  in  your  fingers,  and  a  liquid  is  something  you  can't 
pick  up. 

Tom.    The  real  magic  of  it  is  that  a  piece  of  ice  and  a  spoon- 
ful of  water  are  just  the  same  thing.     The  same  thing  is  differ- 
ent at  different  times  ;   sometimes  it  is 
ice,  and  sometimes  water.     I  wonder  why. 
Let  us  ask  Jack. 

Jack.  I  think  Mary's  definition  is  a 
pretty  good  one  —  a  solid  is  a  thing  you 
can  pick  up  in  your  fingers.  You  can 
change  a  solid  into  a  liquid,  if  you  want 
to,  by  heating  it.  You  can  change  a 
piece  of  ice  into  water  by  letting  it  melt. 
A  little  heat  will  do  it. 

Fred.  How  does  heat  do  it,  Jack  ? 
Solids,  Liquids,  and  Gases  are  made  up  of 
Millions  of  Small  Particles.  —Jack.  Well, 
you  have  to  begin  far  off  if  you  wish  to 
understand.  The  scientific  men  have 
proved  that  all  solids  —  and  all  liquids, 
too  —  are  made  up  of  little  particles 
crowded  close  together.  When  you  heat  a  solid  the  particles 
are  forced  farther  and  farther  apart. 

Heat  makes  Solids,  etc.,  expand.  —  "A  piece  of  solid  iron  gets 
larger  when  you  heat  it.  When  a  blacksmith  wants  to  fit  a 
new  tire  on  a  wheel  he  first  heats  it  and  puts  it  on ;  then  the 
tire,  as  it  gets  cold  again,  shrinks  tightly  on  the  wheel  and 
stays  where  it  was  put." 


FIG.  54 

A  solid,  a  piece  of  iron  for 
instance,  is  made  up  of 
thousands  and  thousands 
of  little  particles,  each 
one  like  every  other  one, 
all  crowded  together,  like 
the  lower  part  of  the  pic- 
ture. When  you  heat  a 
solid  the  little  particles 
are  forced  farther  apart, 
so  that  by  and  by  they 
look  like  the  upper  part 
of  the  picture.  The  solid 
will  get  larger  if  you 
heat  it. 


PHYSICS 


75 


"  Every  little  particle  of  the  tire  has  been  forced  apart  by  the 
heat,  and  by  and  by  the  whole  tire,  which  was  in  the  first  place 
smaller  than  the  wheel,  grows  large  enough  to  slip  over  the 
rim.  Then  the  blacksmith  slips  it  on  and  lets  it  cool.  As  it 
cools,  it  shrinks  and  fits  the  rim  tightly.  The  heat  has  loosened 
the  particles,  you  might  say." 

Agnes.  How  do  you  know  the  particles  are  farther  apart 
when  the  iron  is  hot  ? 

Jack.  There  are  just  so  many  particles  in  the  cold  iron  to 
begin  with,  Agnes  —  say  ten  millions  of  them,  if  you  please. 
And  ypu  haven't  put  any  more  particles  in  the  tire,  you  know ; 


FIG.  55 

The  right-hand  picture  shows  a  wheel  ready  to  be  fitted  with  a  tire ;  the  middle  picture 
shows  the  tire  heated  in  a  fire.  When  the  tire  has  expanded  —  grown  large  — enough 
the  blacksmith  fits  it  on  the  wheel  and  lets  it  shrink  tight  by  cooling. 

you  have  simply  heated  it.  But  the  tire  really  has  grown 
bigger  — the  proof  is  that  it  will  slip  over  the  rim  of  the  wheel. 
The  same  ten  million  little  particles  of  the  cold  iron  fill  a  larger 
space  than  when  they  are  cold ;  so  they  must  have  been  forced 
farther  apart  somehow,  you  see.  And  the  heat  did  it  —  noth- 
ing else  could  have  done  it. 

Mary.    Suppose  you  had  heated  the  iron  more  and  more, 
Jack.     What  then  ? 


76  THE  SCIENCES 

Jack.  If  you  had  put  the  iron  in  a  furnace  and  kept  on 
heating  it,  you  would  have  had  a  hot  solid  at  first ;  then  it 
would  have  become  pasty,  almost  like  dough,  and  by  and  by 
it  would  become  a  liquid  —  it  would  flow  like  water.  You 
cannot  try  the  experiment  with  iron,  but  you  have  often  seen 
the  boys  try  it  with  lead  when  they  are  molding  bullets  for 
their  guns.  Lead  melts  more  quickly  than  iron. 

Agnes.  Yes ;  they  put  the  lead  in  a  ladle  and  melt  it,  and 
then  pour  it  into  molds  and  let  it  cool. 

Jack.  Iron  is  made  up  of  one  kind  of  small  particles,  and 
lead  is  made  up  of  another  kind  of  particles  ;  and  it  takes  less 
heat  to  separate  the  lead  particles.  But  heat  does  the  same 
thing  always.  It  separates  the  particles  farther,  the  more  heat 
you  apply.  First  you  have  a  solid,  and  then  a  liquid  ;  and  if  you 
heat  the  liquid  enough,  you  have  a  gas  —  iron  gas,  lead  gas. 

Tom.  If  you  were  to  go  on  heating  iron  gas  for  a  week, 
what  would  you  get  ?  something  different  from  gas  ? 

Jack.  No;  you  would  get  very  hot  iron  gas  and  nothing 
more.  You  can  have  matter  in  only  three  forms  —  solid,  liquid, 
gas  —  but  you  can  turn  one  form  into  the  other  by  heat  or  by 
cold.  Take  ice,  for  instance. 

Fred.  Ice  is  solid.  If  you  make  it  colder  and  colder,  it  is 
nothing  but  ice  —  the  north  polar  regions  are  ice  and  nothing 
else. 

Agnes.    And  if  you  heat  ice,  it  becomes  water. 

Mary.  And  if  you  heat  water  in  a  teakettle,  it  becomes 
steam. 

Tom.  And  if  you  heat  steam,  Jack,  more  and  more,  is  it 
always  steam  ? 

Jack.  It  is  never  anything  else.  It  is  simply  very  hot  steam. 
The  boiler  of  a  locomotive  or  of  a  steamship  makes  steam  and 


PHYSICS 


77 


nothing  else.  Solid,  liquid,  gas  —  that  is  all  you  can  get.  If 
you  cool  a  gas  like  steam  enough,  you  will  get  a  liquid ;  and  if 
you  cool  a  liquid  enough,  you  will  get  a  solid. 

Most  Gases  are  Invisible.  —  Mary.  I  have  seen  solids  and 
liquids ;  but  I  am  not  sure  I  have  ever  seen  gases. 

Fred.  Well,  you  have  smelled  them,  anyway,  from  leaky  gas 
fixtures  in  the  house,  or  when  the  match  went  out  before  you 
could  light  the  gas  at  the  burner. 

Mary.  Oh,  yes  ;  and  of  course 
there  is  gas  inside  of  the  little 
toy  balloons.  But  I  have  never 
seen  gas. 

Jack.  Most  gases  cannot  be 
seen.  They  are  invisible.  Air 
is  invisible,  but  it  is  all  around 
us.  If  any  one  asked  you  to 
prove  that  air  was  really  all 
around  us,  Mary,  how  would  you 
prove  it  ? 

Mary.  Why,  I  should  say  that 
the  wind  was  nothing  but  mov- 
ing air. 

Jack.    That  is  a  good  way,  my  dear, 
was  n't  blowing  ;  then  what  ? 

Mary.    I  should  wait  till  it  did. 

Jack.  You  could  make  an  experiment  to  prove  it  this  way. 
Take  an  empty  tumbler  and  hold  it  upside  down.  We  call  it 
empty,  but  it  is  really  full  of  air — of  invisible  air.  Then  take 
a  glass  bowl  half  full  of  water  and  float  a  cork  on  it.  Now 
gently  press  the  tumbler  down  over  the  cork  (see  the  picture) 
and  see  what  you  will  see.  If  there  were  nothing  in  the  tumbler 


FIG.  56 

A  glass  bowl  partly  filled  with  water,  a 
cork,  and  a  glass  tumbler  are  needed 
to  prove  that  the  tumbler  was  filled 
with  air.  This  experiment  should  be 
tried  in  the  class  room. 


But  suppose  the  wind 


THE  SCIENCES 


-if  the  tumbler  were  really  empty  —  then  the  water  would 
fill  it  full ;  but  you  can  see  that  the  water  rises  only  for  a 
certain  distance,  and  no  higher.  There  is  air  in  the  tumbler 
still. 

Tom.    I   can   prove   that   there  is  air  in  the  tumbler  now. 
Tip   the    tumbler   sidewise    a    little  while    it    is    in   the   bowl 

and  the  air  will  come  out  in 
bubbles. 

Fred.  What  becomes  of 
the  air  in  the  bubbles  when 
they  come  to  the  surface  ? 

Tom.  Why,  it  just  mixes 
with  the  other  air  all  around 
us. 

The  Diving  Bell.  —  Agnes. 
The  diving  bell  that  men  use 
at  the  bottom  of  rivers  is  like 
the  tumbler,  is  n't  it  ? 

The  Earth's  Atmosphere. — 
Jack.    The  air  is  all  around 
us  everywhere,  for  wherever 
you  go  you  find  air  to  breathe. 
Agnes.    Not  on  the  tops  of  mountains,  Jack. 
Jack.    There  is  not  so  much  air  at  the  tops  of  mountains  as 
there  is  below,  Agnes,  but  there  is  air.     Men  have  climbed  the 
very  highest  mountains,  and  as  they  went  up  they  found  less 
and  less  air.     Birds  fly  nearly  as  high.     The  condor  —  a  bird 
like  an  eagle  —  flies  high  in  the  Andes  of  South  America,  and 
balloons  carrying  men  have  gone  five  miles  high.     Balloons 
without  men  have  gone  as  high  as  ten  miles,  but  the  air  is  so 
thin  at  that  height  that  men  could  not  breathe. 


FIG.  57.  BUBBLES  OF  AIR  ESCAPING 
FROM  THE  MOUTH  OF  A  GOLDFISH 
IN  A  GLOBE 


FIG.  58 

The  diving  bell  is  lowered  by  a  chain  from  a  ship,  and  air  is  pumped  into  it  by  the  pipe 
marked  T  in  the  picture.  The  whole  diving  bell  is  under  wa,ter,  but  the  water  rises 
no  higher  than  its  floor.  The  pressure  of  the  air  keeps  it  out.  A  diver  goes  down  to 
the  bottom  of  the  harbor  and  fastens  ropes  to  whatever  he  wants  to  hoist  to  the  sur- 
face. He  has  a  waterproof  and  air-proof  suit  of  clothes,  and  air  is  pumped  down  for 
him  to  breathe  (through  the  small  pipe  in  the  picture).  The  foundations  for  the  piers 
of  bridges  can  be  laid  by  men  working  in  this  way. 

79 


80  THE  SCIENCES 

Mary.  The  air  gets  thinner  and  thinner  as  you  go  up. 
Where  does  it  stop,  then  ? 

Jack.  We  do  not  know  exactly ;  but  there  is  some  air  —  a 
very  little  —  as  high  as  sixty  miles,  because  shooting  stars 


FIG.  59 

The  Himalaya  Mountains  are  about  five  miles,  and  Mont  Blanc,  in  the  Alps,  is  about  three 
miles  above  the  level  of  the  sea.  A  balloon  carrying  men  has  gone  up  five  miles  and 
very  light  balloons  filled  with  gas  have  gone  nearly  ten  miles  above  sea  level. 

begin  to  burn  as  high  as  that.     They  burn  when  they  first  meet 
the  air,  about  sixty  miles  above  the  ground.1 

Balloons.  —  Tom.    The  balloon  floats  in  the  air  because  it  is 
lighter  than  the  air,  just  as  a  chip  floats  on  the  water. 

1  See  Book  I  (Astronomy),  Meteors,  page  45. 


PHYSICS 


8l 


Mary.  If  the  balloon  is  lighter  than  the  air,  then  the  air 
itself  must  be  heavy ;  for  a  balloon  weighs  a  good  deal,  espe- 
cially when  it  is  carrying  men. 

Air  is  Heavy.  — -Jack.  Yes,  the  air  is  heavy,  and  there  is  a 
simple  way  to  prove  it.  / 

Reservoirs,  Fountains,  and  the  Water  Supply  of  Cities.  —  "  If 
you  have  a  reservoir  full  of  water  and  a  fountain  joined  to 
the  reservoir  by  a  pipe,  the  fountain  will  play  as  soon  as  the 


All  these  glass  vessels  are  joined  together  by  the  brass  tube  at  the  bottom.  If  you  fill  the 
large  jar  at  the  left-hand  side  with  water,  all  the  other  tubes  will  at  once  fill  up  to  the 
same  level.  The  air  presses  on  the  water  in  the  large  jar  and  forces  it  up  into  the  other 
tubes  and  makes  the  little  fountain  play. 

water  is  turned  on,  and  the  fountain  will  play  as  high  l  as  the 
water  in  the  reservoir.  That  is  because  the  air  above  the 
reservoir  is  heavy  and  presses  down  on  the  water  in  it  and 
forces  it  up  in  the  fountain.  (See  Fig.  61.)  Now  here  is  an 

1  Or  nearly  as  high  ;  the  friction  of  the  water  in  the  pipe  makes  some  difference. 


FIG.  61.     RESERVOIRS,  FOUNTAINS,  AND  THE  WATER  SUPPLY  OF  CITIES 

picture  shows  a  lake  which  is  the  source  from  which  the  water  is  obtained.  A  dotted 
line  across  the  picture  marks  the  level  of  the  upper  surface  of  the  lake.  An  aqueduct 
(water  pipe)  takes  the  water  from  the  lake,  carries  it  under  the  hill,  under  a  pond,  up 
another  hill,  where  there  is  a  fountain,  and  delivers  the  water  to  the  city  reservoir. 
From  the  city  reservoir  pipes  conduct  the  water  all  over  the  city  —  to  public  fountains, 
to  the  upper  stories  of  houses,  and  so  forth.  Notice  that  all  the  fountains  send  their 
jets  to  about  the  same  height. 


FIG.  62 

The  U-shaped  tube  is  partly  filled  with  water  as  in  the  right-hand  picture.  Air  fills  the  rest 
of  both  branches  of  the  tube.  Now  tip  the  tube  so  that  one  branch  of  the  tube  shall  be 
completely  filled  with  water  —  water  on  one  side,  air  on  the  other.  Then  cover  the 
water  side  with  your  finger,  as  in  the  left-hand  picture.  You  will  see  that  the  water 
will  stand  at  different  heights  on  the  two  sides.  There  is  air  pressure  on  one  side  of 
the  tube  and  no  air  pressure  on  the  other  (your  finger  keeps  the  air  out).  The  air 
pressure  keeps  the  water  standing  high.  If  you  take  your  finger  away  and  let  the  air 
in,  the  water  on  both  sides  of  the  tube  will  stand  at  the  same  level  on  both  sides. 
(This  experiment  should  be  tried  in  the  schoolroom.) 


82 


PHYSICS 


experiment  that  we  can  try  ourselves  with  this  bit  of  glass  tube 
bent  into  the  shape  of  a  U. 

"  You  see  that  the  air  must  be  heavy ;  it  must  press  down 
with  weight  because  it  makes  the  fountain  play  (Fig.  61)  and 
keeps  the  water  standing  high  (Fig.  62). 

The  Barometer.1  —  "  Instead  of  using  water  in  the  U-shaped 
tubes,  you  can  use  any  liquid  —  milk,  kerosene  oil,  quicksilver. 
It  is  convenient  to  use  quicksilver 
because  it  is  heavy  and  because  it  is 
so  clean.2 

"  You  need  a  hollow  glass  tube 
about  thirty-two  inches  long,  closed 
at  one  end,  a  lot  of  quicksilver,  and 
a  flat  basin  of  glass  or  china.  Hold 
the  long  tube  with  its  open  end 
upwards.  It  is  full  of  air.  Make  a 
paper  funnel  and  pour  quicksilver 
from  a  pitcher  into  the  open  tube, 
slowly  and  carefully,  until  you  have 
quite  filled  it.  As  the  quicksilver 
goes  in  it  will  drive  out  the  air,  and 
finally  you  will  have  a  tube  with  no 

,  .  .  See  the  description  in  the  text. 

air  in  it  —  nothing  but  quicksilver. 

You  must  handle  it  carefully  because  it  is  quite  heavy.     Now 

put  your  finger  over  the  open  end  of  the  long  tube  and  turn 

1  The  barometer  is  an  instrument  to  measure  the  weight  —  the    pressure  — 
of  the  air.     The  name  comes  from  two   Greek  words,  one   meaning  "  weight," 
and  the  other  "  to  measure." 

2  Quicksilver  is  a  poison  if  taken  in  the  mouth ;  it  is  perfectly  safe  to  handle 
it  unless  there  are  open  cuts  on  the  hands  and  fingers.     If  it  touches  a  gold  ring, 
however,  it  will  cover  the  gold  with  a  thin  layer  of  quicksilver  that  will  not  wear 
off  for  some  time. 


FlG.  63.       HOW  TO    MAKE  A 

BAROMETER 


84 


THE   SCIENCES 


the  tube  swiftly  upside  down.  (See  the  left-hand  picture, 
Fig.  63.)  If  you  should  now  take  your 
finger  away,  all  the  quicksilver  would  fall 
out.  There  would  be  nothing  to  support 
it.  But  dip  the  open  end  of  the  long 
tube  in  the  basin  of  quicksilver,  take 
your  finger  away,  and  see  what  happens. 
The  quicksilver  will  fall  in  the  tube  a 
little  distance  —  a  few  inches — and 
then  it  will  stop.  The  air  is  pressing 
on  the  quicksilver  in  the  basin  and  is 
pressing  some  of  it  up  into  the  tube. 
There  is  no  air  above  the  quicksilver  in 
the  tube  ;  nothing  is  pressing  downward 
except  the  weight  of  the  quicksilver  in 
the  tube  itself.  The  weight  of  the 
quicksilver  in  the  tube  pressing  down- 
ward just  balances  tire  pressure  of  the 
air  on  the  quicksilver  in  the  basin.  The 
two  pressures  just  balance  each  other." 
The  Air  presses  about  Fifteen  Pounds 
on  Every  Square  Inch.  —  Tom.  The 
height  of  the  column  of  quicksilver  in 
the  tube  is  about  thirty  inches. 

Jack.  Yes ;  and  if  the  tube  were  an 
inch  square,  the  column  of  quicksilver 
in  it  (thirty  inches  high  and  an  inch 
square)  would  weigh  fifteen  pounds. 
The  air  pressing  on  the  basin  keeps  that 
column  standing.  It  keeps  a  weight  of 
fifteen  pounds  standing. 


FIG.  64.  A  QUICKSILVER 
BAROMETER  READY  FOR 
USE 


The  long  glass  tube  has  a  scale 
of  inches  at  the  upper  end ; 
28,  29,  30,  31  inches  are 
marked,  as  well  as  the  tenths 
of  inches.  The  basin  of 
quicksilver  is  at  the  bottom. 


PHYSICS 


Fred.  That  is  what  is  meant  by  saying,  the  air  presses 
fifteen  pounds  on  every  square  inch  of  your  body,  is  n't  it  ? 

Jack.  It  presses  fifteen  pounds  on  every  square  inch  of  the 
whole  world  ;  on  your  body,  and  on  the  ground,  and  on  the  water 
—  everywhere.  It  presses  down  and  it  presses  up,  too. 

Tom.    How  does  it  press  up?     I  see  that  it  presses  down. 

Fred.  The  air  must  press  up 
or  else  a  balloon  would  not  rise. 

Jack.  That  is  one  proof,  and 
here  is  another  that  you  can  try 
for  yourself.  (See  Fig.  65.) 

How  to  measure  the  Heights  of 
Mountains.  —  "Now  I  want  you 
to  say  what  would  happen  if  I 
had  taken  the  barometer  to  the 
top  of  a  mountain." 

Mary.  The  air  is  lighter  at 
the  top  of  the  mountain  than 
it  is  here,  and  does  not  press 
down  so  much. 

Tom.  So  the  quicksilver  in 
the  tube  would  not  stand  so 
high ;  it  would  not  have  so 
much  air  pressure  to  balance. 

Jack.  Bravo  !  that  is  just  right.  At  the  level  of  the  ocean 
all  the  air  —  the  whole  atmosphere  —  is  above  you,  and  it 
presses  fifteen  pounds  on  every  square  inch  of  the  ground. 
The  quicksilver  stands  thirty  inches  high.  When  you  go  up 
about  1000  feet  the  air  above  you  presses  less  because  there  is 
less  of  it;  you  have  left  1000  feet  of  it  below  you,  and  the 
column  of  quicksilver  is  about  twenty-nine  inches  high  ;  if  you 


FIG.  65 

Fill  (or  partly  fill)  a  tumbler  with  water  and 
press  a  stout  piece  of  writing  paper  over 
the  top  closely.  Put  the  palm  of  your 
hand  over  the  paper  and  hold  it  on  tightly. 
Now  quickly  turn  the  tumbler  upside 
down  and  take  away  your  hand  from  the 
paper.  (See  the  picture.)  The  pressure 
of  the  air  from  below  is  so  much  greater 
than  the  weight  of  the  water,  and  of  the 
small  amount  of  air  in  the  tumbler,  that 
the  paper  will  hold  the  water  up.  (This 
experiment  should  be  tried  in  the  school- 
room.) 


86 


THE   SCIENCES 


go  up  2OOO  feet,  there  is  less  air  above  you  and  the  column  is 
about  twenty-eight  inches  high,  and  so  on. 

Tom.    So  you  could  measure  the  height  of  a  mountain  by 
noticing  the  height  of  the  column  of  quicksilver  in  the  tube  ? 

On  high  mountains  the  column 
would  be  short. 

Jack.  That  is  right,  and  that 
is  the  way  the  heights  of  moun- 
tains are  really  measured.  A 
barometer  measures  the  weight 
of  the  air  above  you.  The 
higher  you  go  the  less  air  above 
you  and  the  less  pressure  on 
the  basin  of  the  barometer. 

The  Barometer  is  a  Weather- 
glass. —  Fred.    Sometimes  we 
FIG.  66.    AN  ANEROID  BAROMETER     see  in  the  newspapers  a  notice 

(A  BAROMETER  WITHOUT  QUICKSILVER)        r  storm 

Aneroid  is  a  Greek  word  that  means  "  with-     T21]rean    oa  Vo 
out  any  liquid."     Inside  of  the  outer  metal 
case  is  a  tightly  sealed  box  containing  no     of   low    barometer    Coming, 
air.     On  this  box  the  outside  air  presses,  r^     jt  happens  that  where 

sometimes   more,   sometimes   less.     The 

little  box  changes  its  shape  under  this    storms  are  the  air  weighs  less 

pressure,  and  things  are  so  arranged  that  ancj     the     barometer     is     low  — 
changes  of  pressure  make  a  needle  pointer  .  r  .... 

move  around  a  dial.     This  form  of  barom-  the     Column     of     quicksilver     IS 

eter  is  very  convenient  for  travelers  and  short.       In     fine      weather      the 

air  is  heavy  and  presses  down 

more ;  so  the  barometer  is  high  and  the  column  of  quicksilver 
is  long.  If  you  watch  the  quicksilver  from  day  to  day,  you  will 
find  this  is  the  case,  generally :  when  fine  weather  is  coming 
or  is  here  the  barometer  is  high;  when  storms  are  coming  or 
are  here  the  barometer  is  low.  So  the  barometer  is  a  kind  of 


FIG.  67 

A  map  made  by  the  Weather  Bureau  one  November  morning.  An  area  of  low  barometer 
was  near  Omaha  and  it  was  moving  towards  Canada  (in  the  direction  of  the  curved 
arrow).  Wherever  there  are  little  dots  observations  had  been  taken  and  telegraphed 
to  Washington.  The  arrows  through  the  dots  fly  with  the  wind  —  they  point  in  the 
direction  of  the  wind's  motion  at  each  place.  Where  the  dots  are  bkck  it  was  raining ; 
where  they  are  square  it  was  snowing ;  where  they  are  circles  with  white  centers  it  was 

cloudy.     The  full  lines  ( )  join  all  places  where  the  barometer  was  at  the  same  height, 

as  30^,  30^5,  30,  29!%  inches.     The  dotted  lines  ( )  join  all  the  places  where 

the  thermometer  stood  the  same,  as  70°,  60°,  50°,  40°,  30°,  20°,  10°,  o°.  There  was 
zero  weather  near  the  Rocky  Mountains,  while  it  was  warm  and  cloudy  east  of  the  Alle- 
ghenies.  Northwest  of  the  area  of  low  barometer  there  was  snow ;  southeast  of  it  there 


88  THE  SCIENCES 

weatherglass.  It  tells  you  beforehand  what  kind  of  weather 
is  coming.1 

Fred.    And  it  tells  ships  at  sea  when  to  look  out  for  storms. 

United  States  Weather  Bureau  Predictions. — Jack.  Every 
day  at  a  hundred  places  in  the  United  States,  in  Cuba,  and 
so  forth,  the  observers  of  the  Weather  Bureau  notice  how 
their  barometers  are  standing  and  telegraph  to  the  central 
Weather  Bureau  at  Washington.  There  they  make  a  weather 
map  of  the  whole  country  several  times  daily.  If  a  storm  is 
traveling  eastwards,  it  will  show  on  the  map  by  an  area  of  low 
barometer,  as  they  call  it.  The  barometer  in  the  country  round 
Omaha  will  be  low  on  Monday,  for  instance ;  by  Tuesday  the 
storm  has  traveled  to  Buffalo ;  so  the  Weather  Bureau  tells 
New  York  to  look  out  for  a  storm  on  Wednesday. 

Agnes.    Well,  I  never  knew  before  how  that  was  done. 

Thermometers.2—  Fred.  A  thermometer  has  quicksilver  in 
it,  too,  but  it  is  closed  at  both  ends. 

Tom.  A  thermometer  is  to  measure  how  hot  the  air  is.  It 
is  different  from  a  barometer ;  that  measures  how  heavy  the 
air  is. 

Jack.  Yes,  a  thermometer  measures  how  hot  the  quicksilver 
in  it  happens  to  be  by  the  height  of  the  quicksilver  in  the  glass 
tube.  If  the  quicksilver  column  is  long,  then  the  temperature 

1  Barometers  often  have  words  engraved  opposite  points  of  their  scales ;  as : 
30^   inches,    set  fair   (meaning   that    the    weather  will  be  fair  for  some  time); 
30  inches,  fair ;   2<)\  inches,  change  (meaning  expect  a  change  soon);   29,  rain  ; 
28^,  much  rain  ;  28,  stormy.     The  weather  is  foretold  by  a  change  in  the  barome- 
ter rather  than  by  the  actual  height  of  the  quicksilver.     If  the  quicksilver  is  rising, 
then  the  weather  is  changing  towards  fair ;  if  it  is  falling,  then  the  weather  is 
changing  towards  stormy. 

2  The  word  thermometer  is  from  two  Greek  words,  and  it  means  "  an  instru- 
ment to  measure  heat  —  temperature." 


PHYSICS 


89 


100* 


is  high  ;  if  the  column  is  short,  then  the  temperature  is  low. 
The  higher  the  temperature  the  longer  is  the  quicksilver  column. 

Mary.    It   is   like   the    iron   tire    of    the    cart   wheel.      (See 
Fig.   55-)      The    hotter    the    fire,   the  b 

longer  the  tire  is. 

Agnes.  ^  By  just  putting  my  hand  on 
a  thermometer  I  can  make  the  quick- 
silver mount  up  in  the  tube. 

Tom.  Jack,  why  do  they  make  the 
scale  this  way  ?  32°  is  marked  freezing, 
and  212°  is  marked  boiling. 

Jack.  A  German  named  Fahrenheit l 
invented  the  thermometer  we  use  about 
200  years  ago.  (See  the  right-hand 
picture  in  Fig.  68.)  He  put  his  ther- 
mometer into  melting  ice  and  made  a 
mark  on  the  tube  just  where  the  quick- 
silver stood ;  and  then  into  boiling 
water  and  made  a  mark  on  the  tube 
where  the  quicksilver  stood.  It  is  too 
complicated  to  tell  you  why  he  named 
the  first  mark  32°  and  the  second 
212°,  but  anyhow  he  did  so.  The  dis- 
tance between  his  two  fixed  marks  he 
divided  into  1 80  equal  parts  —  degrees. 
His  thermometer  was  used  in  Eng- 
land ;  the  Pilgrims  brought  it  over  to 
America  ;  and  we  use  it  to-day.  But 
there  is  another  scale  of  degrees  —  the  centigrade2  (see  the 
left-hand  picture  in  Fig.  68)  —  which  was  invented  in  France 

1  Pronounced  far'en-hlt.  2  Pronounced  sen'ti-grad. 


0*1*1— 


-17.S* 


FIG.  68.  THE  GLASS  TUBES 
OF  Two  THERMOMETERS 

The  tubes  are  closed  at  both  ends, 
are  entirely  empty  of  air,  and 
are  partly  filled  with  quicksilver. 


90  THE   SCIENCES 

about  a  hundred  years  ago,  that  is  used  nearly  everywhere  in 
Europe.  On  the  centigrade  thermometer  the  freezing  point 
is  marked  zero  degrees  (o°),  and  the  boiling  point  of  water 
one  hundred  (100°) ;  and  the  scale  between  o  and  100  is  divided 
into  equal  parts.  Zero  of  Fahrenheit's  scale  is  17^5-  degrees 
below  zero  of  the  centigrade  scale.  (See  Fig.  68.) 

Mary.   Was  Centigrade  a  man  ? 

Tom.  Of  course  not;  don't  you  see  that  centi  means  "one 
hundred,"  and  grade  "  degree  "  ? 

Mary.  Why,  certainly  ;  I  thought  he  might  be  a  Frenchman 
though. 

Jack.  If  you  put  one  of  our  thermometers  into  melting  ice,  it 
will  always  mark  32°  ;  if  you  put  it  in  boiling  water,  it  will  always 
mark  212°  ;  and  if  you  put  the  bulb  of  it  in  your  mouth,  it  will 
always  mark  about  98°  — that  is,  unless  you  have  a  fever. 

Fred.  The  doctor  always  takes  my  temperature  with  a  little 
thermometer  when  I  am  ill. 

Tom.  And  if  your  temperature  goes  as  high  as  104°,  he 
looks  very  serious.  The  sign  of  being  well  is  to  have  a  tem- 
perature of  98°,  they  say. 

Steam.  — Jack.  If  you  took  a  teakettle  and  boiled  the  water 
in  it,  the  temperature  of  the  boiling  water  would  be  212°. 
Inside  the  kettle  there  is  water  at  the  bottom,  and  above  the 
water  there  is  steam.  If  we  had  a  glass  kettle,  you  could  look 
through  the  sides  and  you  would  see  nothing  at  all  above  the 
water.  True  steam  is  invisible ;  but  there  is  steam  there  all 
the  while.  How  do  we  know  ? 

Mary.  We  see  the  steam  lift  the  lid  of  the  kettle  every  now 
and  then. 

Fred.  I  thought  steam  was  visible.  What  is  that  cloud 
coming  out  of  the  nozzle  of  the  kettle  ? 


PHYSICS 


Jack.  That  is  water ;  cooled  steam  ;  water  in  small  drops 
like  fog  or  clouds.  The  real  invisible  steam  is  inside,  trying 
to  lift  the  lid  and  escape.  If  we  fastened  the  lid  down  and 
closed  the  nozzle,  we 
should  have  a  little 
steam  engine. 

The  Steam  Engine. 
—  Then  Jack  ex- 
plained the  working 
of  the  steam  engine 
to  the  children  in  this 
way.  (See  Fig.  70.) 

F  is  the  fire  box  ; 
B  is  the  boiler  with 
water  in  the  bottom 
of  it,  and  steam  at  the 
top;  S  is  the  steam 
pipe  that  carries  the 
live  steam  over  to 
the  valve  chest  VC. 
There  are  two  pipes 
in  the  valve  chest, 
pipe  M  and  pipe  N, 
and  both  pipes  open 


FIG.  69. 


A  TEAKETTLE  WITH  BOILING 
WATER  IN  IT 


It  gives  out  clouds  of  what  we  call  steam.  The  clouds  are 
really  not  steam,  but  steam  cooled  back  into  water.  If 
you  hold  an  alcohol  lamp  under  the  cloud,  the  hot  flame 
will  turn  it  back  into  steam  and  you  will  see  no  cloud 
over  the  flame,  because  true  steam  is  invisible.  It  is 
there  though,  as  you  can  tell  by  holding  a  cold  spoon 
over  the  invisible  spot.  The  invisible  steam  will  turn 
into  visible  water  (like  fog  or  cloud)  and  gather  in  drops 
on  the  spoon.  (This  experiment  should  be  tried  in  the 
schoolroom.) 


from  the  valve  chest 
and  run  to  the  cylinder  C.  But  things  are  so  arranged  that  both 
pipes  M  and  N  cannot  be  open  at  the  same  time.  If  N  is  open, 
Mis  shut  (as  in  the  picture).  If  Mis  open,  N  must  be  shut. 

The  picture  is  drawn  with  the  pipe  N  open.  The  live 
steam  rushes  into  the  pipe  N,  fills  it,  and  rushes  into  the 
right-hand  end  of  the  cylinder  C  and  presses  against  the  piston 


92  THE   SCIENCES 

head  P.  (The  piston  head  is  a  large  iron  disk  that  fills  up 
the  whole  of  the  diameter  of  the  cylinder.)  The  pressure  of 
the  live  steam  moves  the  piston  head  P  (to  the  left  in  the  pic- 
ture) to  the  other  end  of  the  cylinder  C  and  pushes  the  piston 
rod  R  against  the  crank  G  on  the  crank  shaft  A,  and  turns  it. 
You  must  imagine  now  that  the  piston  head  P  is  at  the 


FIG.  70 
Drawing  of  part  of  a  steam  engine. 

left-hand  end  of  the  cylinder  C  and  that  the  live  steam  fills  the 
whole  of  the  cylinder.  Find  the  letter  Rf  in  the  picture.  R1 
is  fastened  to  a  slide  valve  Fat  one  end  and  to  the  crank  shaft 
at  //",  and  things  are  so  arranged  that  now  the  rod  R'  closes  the 
pipe  N  by  which  the  steam  came  in  and  at  the  same  time  opens 
the  pipe  M.  The  live  steam  is  filling  the  valve  chest  VC  all 


PHYSICS  93 

this  time.  It  cannot  get  into  the  pipe  A7"  (which  is  now  closed), 
and  so  it  rushes  into  the  pipe  M  (which  is  now  open)  and 
presses  against  the  left-hand  side  of  the  piston  head  P  (which 
is  now  at  the  left-hand  end  of  the  cylinder  C}.  The  piston 
is  now  pushed  back  by  the  steam  to  where  it  started  from 
(just  as  in  the  picture),  and  the  crank  shaft  A  is  turned  still 
more.  When  the  piston  gets  back  to  where  it  started  the  pipe 
M  is  closed  and  the  pipe  N  is  opened  again  (by  the  rod  R')  and 
the  piston  head  is  moved  to  the  left  again,  then  to  the  right, 
then  to  the  left,  and  so  on  as  long  as  the  engine  is  running. 
Every  time  the  piston  head  P  travels  the  length  of  the  cylinder 
C  the  crank  G  makes  half  a  turn,  and  in  this  way  the  crank 
shaft  GA  keeps  on  turning.  W  is  a  little  pulley  wheel  fastened 
to  the  crank  shaft ;  and  if  you  put  a  leather  belt  on  this  pulley 
wheel,  you  can  carry  the  power  of  the  engine  wherever  you 
like.  You  can  carry  it  as  far  as  the  belt  goes  and  drive  any 
other  machine  —  a  lathe,  a  saw,  a  drill.  W  is  a  heavy  fly 
wheel  fastened  to  the  shaft  A  to  keep  the  motion  steady. 

All  this  description  of  how  an  engine  works  is  perfectly  easy 
to  understand  if  you  take  one  thing  at  a  time  and  pay  attention  ; 
but  it  is  rather  long,  and  you  had  better  read  it  over  again  care- 
fully with  a  pin  in  your  hand  to  point  with.  The  live  steam  starts 
from  the  boiler  B  (put  your  pointer  there)  ;  fills  the  valve 
chest  VC  (put  your  pointer  there) ;  rushes  through  the  pipe  N 
(point  at  it)  ;  presses  against  the  piston  head  P  (point  at  it)  ; 
drives  the  piston  head  to  the  left-hand  end  of  the  cylinder 
(point  at  it)  ;  moves  the  stiff  piston  rod  R  so  as  to  turn  the 
crank  G  (point  at  R  and  G).  At  this  time  the  pipe  N  is 
closed  and  the  pipe  M  is  open  (point  at  A7"  and  M)  ;  the  live 
steam  is  all  the  while  filling  the  valve  chest  VC  (point  there) 
and  cannot  escape  through  the  pipe  N  (which  is  closed)  and 


94 


THE  SCIENCES 


now  rushes  through  the  pipe  M  (which  is  now  open),  and  so 
on.  You  must  go  through  the  whole  description  again  and 
again  till  you  understand  it. 

The  Locomotive.  —  Figs.  70  and   71    show  just   how  steam 
from  a  boiler  can  be  made  to  turn  a  crank  shaft  (G  in  both 


FIG.  71.     A  STATIONARY  STEAM  ENGINE 

C,  cylinder ;  P,  piston ;  JR,  piston  rod.     The  reader  should  trace  the  course  of  the  steam 
(which  enters  through  the  pipe  S)  throughout  a  complete  motion  of  the  piston. 

pictures)  round  and  round.      Suppose  we  put  wheels  on  this 
crank  shaft  and  make  the  engine  into  a  locomotive. 

In  Fig.  72  you  should  put  your  pointer  on  the  sleepers, 
the  rail,  the  front  wheels  P,  the  front  driving  wheel,  the  fire 
box  A,  the  fuel  grate  R,  the  boiler  G,  the  valve  chest  C, 
the  cylinder  B  (there  is  a  separate  picture  of  the  cylinder  above 
the  main  picture),  the  smokestack  E,  the  cowcatcher,  the  head- 
light, the  bell,  the  sand  box  M  (the  sand  box  is  used  to  hold  sand 
to  sprinkle  on  the  rails  when  they  are  wet  and  slippery,  so  that 
the  driving  wheels  may  not  slide  on  the  track),  the  whistle  O, 
and  the  cab.  The  to-and-f ro  motion  of  the  piston  in  the  cylinder 


96  THE  SCIENCES 

moves  the  driving  wheels  round  ;  the  engine  moves  forward  as 
they  move  round,  and  the  train  follows  the  engine. 

All  steam  engines  work  very  much  like  the  ones  shown  in 
the  pictures.  You  can  see  them  at  work  in  factories,  on  ships, 
in  locomotives,  in  automobiles  —  everywhere.  With  a  machine 
like  this  you  can  take  a  little  water  and  a  little  coal  and  turn 


FIG.  73.     AN  OCEAN  STEAMSHIP 

them  into  a  power  that  will  drive  a  locomotive  sixty  miles  an 
hour,  or  a  great  ship  twenty-five  miles  an  hour  from  New  York 
to  Liverpool. 

Light. — Jack.  The  very  first  thing  to  know  about  light  is 
that  it  travels  in  straight  lines.  You  cannot  see  round  a 
corner,  you  know,  though  you  can  hear  round  a  corner. 

The  room  was  darkened,  and  the  sun's  rays  were  let  in  through 
a  very  small  hole  in  a  card  and  made  an  oval  spot  on  the  floor. 
Tom  took  a  newspaper,  crumpled  it  up,  and  set  it  on  fire  in 


PHYSICS  97 

a  coal  hod,  so  that  the  room  was  partly  filled  with  smoke  and 
dust.  This  made  it  easy  to  trace  each  little  sunbeam  along 
its  whole  course,  as  the  picture  shows. 

Fred.    That  spot  on  the  floor  looks  like  a  picture  of  the  sun. 

Jack.  It  is  a  picture  —  an  image  —  of  the  sun.  It  is  oval 
because  the  sunlight  falls  slanting  on  the  floor.  But  take  this 


FIG.  74 

The  sun's  rays  travel  in  straight  lines.     (This  experiment  should  be 
tried  in  the  schoolroom.) 

large  sheet  of  white  pasteboard  and  hold  it  perpendicular  to 
the  sun's  rays  and  you  will  get  a  round  image.  You  can  get 
a  picture  of  the  landscape  outside  by  letting  light  in  through 
a  small  hole  in  the  same  way.  (See  Fig.  75.) 

Mary.    Well,  I  'm  sure  I  don't  understand  how  you  can  get 
a  picture  of  out-of-doors  by  just  letting  light  through  a  hole. 


98 


THE  SCIENCES 


Jack.  It  is  the  easiest  thing  in  the  world  to  understand  when 
it  is  explained ;  but  it  is  not  so  easy  to  understand  it  when  you 
see  it  the  first  time,  as  you  have,  Mary  —  when  it  is  sprung  on 
you,  as  the  boys  say. 

Fred.  Well,  Jack,  how  is  it  ?  Explain  it  to  us,  now  that 
you  have  sprung  it  on  us. 

Jack.  It  all  comes  from  light  traveling  in  straight  lines.  Let  us 
begin  with  a  simple  case,  and  explain  the  harder  one  afterwards. 


FIG.  75.    A  PICTURE  OF  THE  LANDSCAPE  FORMED  INSIDE  A  DARK  ROOM 
(Camera  obscura)  BY  LIGHT  THAT  PASSES  THROUGH  A  VERY  SMALL  HOLE 

This  experiment  ca  n  be  tried  in  the  schoolroom.  The  room  should  be  quite  dark.  The  hole 
should  be  pierced  in  a  sheet  of  cardboard  or,  better,  a  neat  hole  should  be  drilled  in  a 
sheet  of  tin. 


FIG.  76 

The  light  of  a  candle  travels  in  straight  lines.  Until  you  have  the  candle  (C)  and  the  two 
holes  (A  and  B}  in  the  same  straight  line  you  cannot  see  the  flame.  (This  experiment 
should  be  tried  in  the  schoolroom.) 


FIG.  77 

Some  of  the  rays  from  three  points  of  a  candle  flame  are 'drawn  in  this  picture.  They  fall 
on  a  screen  (a&)  and  make  it  bright.  From  every  point  of  the  flame  there  are  such 
rays.  And  there  are  many  more  than  are  drawn  in  the  picture. 

99 


100  THE  SCIENCES 

The  light  of  the  candle  (Fig.  76)  travels  in  straight  lines. 
So  does  the  light  from  every  brilliant  thing.  Every  point  of 
the  sun  and  every  part  of  a  candle  flame  is  always  sending  out 
rays  of  light,  and  the  rays  go  off  in  every  possible  direction. 

If  you  take  a  pincushion  shaped  like  a  ball  and  stick  it  full  of 
pins  so  that  the  pins  stand  out  all  over  it  everywhere,  that  might 


FIG: 78 

In  a  dark  room  a  candle  shining  through  a  pin  hole  will  form  its  own  image  on  a  screen. 

serve  as  a  model  of  a  brilliant  point  of  a  candle  flame.  Every  such 
point  sends  out  rays  of  light  in  every  direction  —  up,  down,  side- 
wise.  You  "see  "  by  the  rays  that  happen  to  come  your  way. 
Rays  of  light  from  the  candle  flame  go  out  in  every  possible 
direction.  How  do  you  know  that,  Tom  ? 


PHYSICS 


101 


Tom.  Because  you  can  see  the  candle  flame  no  matter  what 
part  of  the  room  you  are  in.  If  you  see  it,  you  must  get  rays 
from  it. 

Jack.  Exactly  ;  now  most  of  the  rays  from  the  flame  light 
up  the  card  and  the  table  and  the  walls  of  the  room ;  a  few  of 
them — only  a  few — get  through  the  hole  in  the  card  (Fig.  78). 
Some  ray  from  the  top  of  the  flame  gets  to  the  hole,  goes 
through  it,  and  goes  on  till  it  meets  the  screen  of  white  paste- 
board. There  it  stops,  and  there  you  have  an  image  of  the 
top  of  the  flame.  Some  ray  from  the  candle  wick  gets  through 
the  hole  and  goes  on  to  meet  the  screen  and,  when  it  meets 
it,  forms  an  image  of  the  wick. 
Some  rays  from  each  of  the 
other  parts  of  the  flame  get 
through  the  hole  and  make 
images,  so  that  finally  an  image 
of  the  whole  flame  is  shown 
on  the  screen.  The  image  of 
the  flame  is  built  up  of  hun- 
dreds of  little  separate  images,  FlG 


The  image  of  candle  shining  through  a  pin 
hole  is  formed  upside  down  on  a  screen, 
and  this  drawing  shows  why. 


you  see.1 

Agnes.  The  image  of  the 
candle  on  the  screen  is  upside 
down,  and  so  was  the  picture  of  the  landscape  (Figs.  75  and  78). 

Jack.   You  can  see  why  it  was  so  from  this  drawing,  Agnes. 

Shadows. —  "The  shadow  of  any  square  or  cube  is  bounded 
by  straight   lines   (Fig.  78),   and    this    is  another  proof  that 


1  The  reader  should  lay  a  straight  edge  (the  edge  of  a  card  will  do)  on  Fig.  78. 
He  will  see  that  the  wick,  the  hole,  and  the  image  of  the  wick  are  in  one  straight 
line.  Again,  the  top  of  the  flame,  the  hole,  and  the  image  of  the  top  of  the  flame 
are  in  one  straight  line,  and  so  on. 


102  THE  SCIENCES 

light  travels  in  straight  lines.  When  the  point  of  light  is  really 
a  point,  or  when  it  is  only  a  small  spot  (as  in  the  electric  street 
lamp)  the  edges  of  the  shadow  are  sharp ;  but  when  the 

light  comes  from  a  large  body  like 
the  sun  the  true  shadow  (the  umbra) 
is  bordered  by  a  less  dark  shadow 
(the  penumbra).  If  you  hold  a  piece 
FlG- 8o  of  cardboard  in  front  of  a  lighted 

A  point  of  light  at  A  lights  half  of  a    candle  in  a  dark  room,  you  can  see 
globe  at  B,  and  B  casts  a  shadow.    the  shadow  of  the  cardboard  on  the 

The  electric  street  lamp  casts  a 

shadow  with  sharp  edges  as  in  the    wall.    The  shadow  is  made  up  of  two 
picture,  because  the  light  of  an    parts  —  tne  ^ark  center  (\ht-umbra) 

electric  street  lamp  comes  from  a 

very  small  spot -a  point  of  light,  and  a  less  dark  part  (fat  penumbra). 

Move  the  cardboard  till  it  is  quite 

near  the  wall  and  you  will  see  the  umbra  get  dark  and  sharp 
and  the  penumbra  almost  disappear."  l 

Eclipses  of  the  Sun  and  Moon.  —  Eclipses  of  the  sun  and  moon 
can  be  explained  by  Fig.  8 1 .  The  globe  of  the  lamp  stands  for 
the  sun,  the  ball  B  for  the  earth,  the  ball  C  for  the  moon. 

Suppose  you  were  on  the  earth  (B)  inside  the  shadow  of  the 
moon.  (Take  a  pin  and  point  out  the  place.)  The  sun  would  be 
hidden  from  you  if  you  were  there ;  the  sun  would  be  eclipsed 
to  you.  An  eclipse  of  the  sun  occurs  for  any  place  on  the  earth 
when  that  place  is  in  the  moons  shadow.  (See  Fig.  51.) 

The  moon  revolves  around  the  earth,  you  know.  Take  the 
little  ball  C  and  suspend  it  on  that  side  of  the  ball  B  which  is 
farthest  from  the  lamp.  It  will  be  in  the  shadow  of  the  ball  B. 
When  the  moon  is  in  the  shadow  of  the  earth  no  light  from 

1  This  experiment  should  be  tried  in  the  darkened  schoolroom.  When  the 
appearances  are  thoroughly  understood  a  second  candle  should  be  lighted  and 
the  shadows  of  the  two  made  to  overlap. 


FIG.  8 1 

A  schoolroom  experiment  on  shadows.  The  room  must  be  dark  and  the  lamp  should  have 
a  ground-glass  globe.  The  ball  B  may  be  an  orange  fastened  to  a  pincushion  by  a 
knitting  needle.  The  little  ball  C  (a  small  ball  of  twine)  can  be  suspended  by  a  string 
so  as  to  cast  a  shadow  on  the  globe  B.  Notice  that  the  ball  C  has  two  shadows,  a 
dark  central  shadow  (the  umbra)  and  a  less  dark  shadow  around  it  (the  penumbra). 
The  large  brilliant  globe  of  the  lamp  makes  two  shadows  to  C.  (By  a  little  thinking 
you  can  see  why.) 


FIG.  82 

A  beam  of  light  enters  a  dark  room  through  a  hole  in  the  wall  (A)  and  falls  on  a  mirror  at 
B.  It  is  reflected  from  the  mirror  upwards  to  form  a  spot  on  the  ceiling  at  C.  By  put- 
ting a  pencil  vertically  at  B,  in  the  line  £D,  you  will  see  that  the  ray  of  light  AB 
and  the  ray  of  light  BC  make  the  same  angles  with  the  pencil  BD.  That  is,  the  angles 
ABD  and  CBD  are  always  equal  to  each  other,  no  matter  where  the  mirror  may  be. 

103 


104 


THE  SCIENCES 


the  sun  can  reach  it,  and  it  is  eclipsed.     An  eclipse  of  the  moon 
occtirs  whenever  the  moon  is  in  the  shadow  of  the  eartJi. 

Reflection  of  Light.  — Jack.    Light  that  falls  on  any  surface  is 
reflected  from  it.     That  is  the  way  we  see  the  surface.     The 

sunlight  falls   on   the  ground 
and    is    reflected    up    to    our 


eyes, 


else  we   should  not   see 


FIG.  83 


the  ground.  A  feather  that 
is  floating  in  the  air  reflects 
light  to  us,  else  we  should 
not  see  it.  The  moon  float- 
ing in  the  sky  reflects  the 
sunlight  to  us,  else  we  should 
not  see  it. 

Fred.  The  sun  sends  us  its 
own  light  though.  We  do 
not  see  it  by  reflected  light. 

Jack.  The  sun,  the  stars,  an 
electric  lamp,  a  candle,  have 
light  of  their  own.  They  send 
us  light  directly.  The  moon, 


A  ray  of  sunlight  enters  a  dark  room  through  ^      planets    distant  mountains 
a  hole  in  the  wall,  and  it  falls  on  water  con- 

tained in  a  box  with  glass  sides  (a  box  with  and     clouds,     near-by     houses 

one  glass  side  will  do).     The  ray  is  bent  and     rQcks     anj    fieJds,     reflect 

(refracted)  as  soon  as  it  enters  the  water.  * 

sunlight  to  us.     If  you  could 
shut  off  the  sunlight,  you  would  not  see  them. 

Tom.  The  sunlight  is  shut  off  at  night  (at  least  it  is  shut  off 
from  everything  on  the  earth)  and  you  do  not  see  the  moun- 
tains and  the  houses  then.1 


1  The  reasons  why  you  see  the  moon  and  the  planets  at  night  are  explained  in 
Book  I  (Astronomy),  page  33. 


PHYSICS 


105 


Refraction  of  Light.  — Jack.  Light  always  travels  in  straight 
lines ;  but  when  a  ray  of  light  that  has  been  traveling  along 
one  straight  line  in  the  air  enters  something  different  from  air 
—  water  or  glass,  for  instance  —  it  is  bent  (refracted)  into 
another  line.  This  second  line  is  straight,  too ;  but  it  is  not 
the  same  line  as  the  first 
one. 

Water  will  bend  a  ray  of 
light,  and  so  will  glass.  You 
know  what  a  prism  is  ?  A 
glass  pendant  to  a  chandelier 
is  a  prism,  for  instance. 

If  you  let  sunlight  pass 
through  a  prism  and  then 
fall  on  a  sheet  of  paper,  you 
will  get  a  beautiful  spectrum 
of  all  the  colors  of  the  rain- 
bow. If  a  plate  of  glass  or 
a  metal  mirror  is  ruled  with 
fine  parallel  lines  equally 
distant,  say  1000  or  10,000 
to  the  inch,  you  can  get  a  beautiful  spectrum  by  laying  it  out 
in  the  sunshine.  The  colors  of  mother-of-pearl  are  made  in 
this  way.  The  inside  of  the  oyster  shell  is  made  up  of  very 
fine  parallel  ridges,  and  the  light  reflected  from  them  is  scat- 
tered into  a  spectrum  of  colors.  You  can  prove  that  it  is 
the  ridges  that  make  the  colors  by  taking  an  impression  of 
the  inside  of  the  mother-of-pearl  shell  in  wax.  The  wax 
gives  just  the  same  colors.  The  scattering  of  sunlight  by 
raindrops  in  somewhat  the  same  way  has  to  do  with  forming 
the  rainbow. 


FIG.  84 

A  straight  stick  partly  out  of  water  and  partly 
in  the  water  looks  as  if  it  were  bent  just  where 
it  enters  the  water.  Of  course  it  is  not  really 
bent,  but  it  looks  so.  Try  the  experiment 
with  a  pencil  in  a  shallow  basin  full  of  water. 


106  THE  SCIENCES 

Lenses. — "Pieces  of  glass  of  certain  shapes  are  called  lenses.  We 
use  them  to  make  magnifying  glasses,  spectacles,  microscopes, 
telescopes.  You  children  had  better  get  some  old  spectacle 
glasses  and  try  experiments  with  them.  (See  Figs.  45,  88-90.) 


FIG.  85 

A  glass  prism  is  mounted,  for  convenience,  on  a  stand ;  but  the  experiment  can  be  tried  by 
a  prism  held  in  the  hand.  The  candle  flame  seen  through  the  prism  seems  to  be  in  a 
different  place  from  the  real  candle  flame,  because  the  rays  of  light  sent  out  by  the 
flame  are  bent  by  the  prism  and  when  they  come  to  the  eye  they  seem  to  come  from  a 
place  where  the  real  candle  is  not. 


PHYSICS  107 

"  Two  (or  more)  lenses  used  together  make  a  telescope,  you 
know.1  Convex  lenses  concentrate  the  light  that  falls  on  them 
(Fig.  89),  and  concave  lenses  disperse  the  light  that  falls  on 


FIG.  86 

A  beam  of  sunlight  (white  light)  is  separated  by  a  prism  into  rays  of  violet,  indigo,  blue, 
green,  yellow,  orange,  and  red,  and  most  of  the  heat  in  the  beam  falls  near  the  red  end 
of  the  spectrum.  The  heat  rays  are  invisible. 


FIG.  87.     GLASS  LENSES  OF  DIFFERENT  SHAPES 

The  three  to  the  left  of  the  middle  of  the  picture  are  convex  lenses ;  the  other  three 
are  concave  lenses. 

them.     Persons  who  are  nearsighted  use  concave  lenses  in  their 
spectacles,  and  persons  who  are  farsighted  use  convex  lenses." 

1  See  Book  I  (Astronomy),  page  58. 


FIG.  88 

A  convex  lens  in  a  dark  room  will  make  a  sharp  image  of  a  candle  flame  on  the  wall 
if  the  lens  is  at  the  right  distance.  (The  distance  to  the  wall  must  be  different  for 
different  lenses  and  can  be  found  by  trial.) 


FIG.  89 
A  convex  lens  concentrates  light  falling  on  it  to  a  focus  (at  F  in  the  picture). 


FIG.  90 

A  concave  lens  disperses  light  falling  on  it.     (The  light  comes  from  F  in  the  picture 
and  is  dispersed  by  the  lens.) 

108 


FIG.  91.     A  POWERFUL  MICROSCOPE 

The  object  to  be  examined  is  placed  on  the  stand  S  and  looked  at  through  the  long  tube. 
Light  can  be  thrown  on  the  object  by  the  lens  N  or  by  the  mirror  M.  The  right- 
hand  picture  shows  the  way  the  lenses  are  arranged  in  the  tube.  The  eye  is  placed 
near  //,  and  there  is  one  lens  there,  another  at  «,  and  three  others  at  O  (an  enlarged 
picture  of  these  three  is  given  at  Z.).  Such  a  microscope  as  this  can  be  arranged  so 
as  to  magnify  about  2000  times  —  to  make  things  seem  2000  times  larger. 


109 


HO  THE  SCIENCES 

SOUND 

Velocity  of  Sound  and  Light.  —  The  children  were  sitting 
on  the  porch  one  afternoon  when  they  heard  the  church  bell  in 
the  village  ringing. 

Agnes.  Listen  to  the  bell !  how  plainly  you  can  hear  it,  and 
yet  it  is  nearly  three  miles  away. 

Mary.  Two  —  three  —  four.  It  is  four  o'clock.  The  ham- 
mer has  just  this  moment  struck  the  bell. 

Fred.  You  mean  the  hammer  struck  the  bell  a  moment  ago, 
and  we  have  heard  it  this  minute. 

Mary.    Why  do  you  say  that,  Fred  ?    , 

Fred.  You  know  that  you  do  not  hear  the  sound  of  a  blow 
when  the  blow  is  struck  —  not  till  afterwards.  Have  n't  you 
ever  seen  a  gun  fired  by  a  man  a  mile  away  from  you  and  then 
waited  to  hear  the  sound  ? 

Mary.    Why  do  you  have  to  wait  ? 

Fred.  Why,  you  know  the  light  of  the  flash  comes  to  you 
instantly — the  very  minute  the  gun  is  fired;  and  it  takes 
time  for  the  sound  to  travel.  Let  us  ask  Jack  to  tell  us  how 
fast  sound  travels ;  he  is  sure  to  know. 

Jack.  Light  travels  almost  infinitely  fast  j1  but  sound  moves 
much  slower  —  about  noo  feet  in  a  second.  It  takes  sound 
nearly  five  seconds  to  go  a  mile. 

Mary.  Do  you  mean,  Jack,  that  we  did  n't  hear  the  village 
clock  strike  till  fifteen  seconds  after  it  had  really  struck? 

Jack.  Yes  ;  the  hammer  struck  the  bell  first  and  set  it 
vibrating ;  then  the  air  round  the  bell  began  to  vibrate,  and 
the  sound  began  to  travel  off  in  every  direction  —  north,  east, 

1  The  velocity  of  light  is  186,330  miles  in  a  second  of  time.  Light  travels 
from  the  sun  to  the  earth  in  500  seconds,  a  little  more  than  eight  minutes. 


PHYSICS  1 1 1 

south,  west.  If  you  had  been  in  the  village,  you  would  have 
heard  the  bell  the  moment  it  was  struck  ;  if  you  had  been  a  mile 
away,  you  would  have  heard  it  five  seconds  late ;  and  as  we  are 
three  miles  away,  we  all  heard  it  about  fifteen  seconds  later. 


FIG.  92.     A  CHURCH  BELL 
It  is  rung  by  the  rope  that  you  see  on  the  left-hand  side  of  the  picture. 

Tom.  It  is  something  like  throwing  a  stone  into  a  pond  of 
water.  Little  waves  travel  in  every  direction  from  the  place 
where  the  stone  went  into  the  pond. 


112  THE  SCIENCES 

Jack.    Yes ;  and  you  remember  that  the  waves  get  smaller 
and  smaller  the  farther  they  go.      Sound  is  like  that.     The 
vibrations  of  the  air  are  powerful  near  the  sounding  bell,  but 
they  get  weaker  and  weaker  as  you  go  away  from  it. 
Tom.    So  sound  is  a  vibration  is  it,  Jack? 

Jack.    There  would    be  no  sound   unless   there   were   some 
vibration  in  the  first  place.     But  there  wouldn't  be  any  sound 


FIG.  93 

A  wave  of  sound  if  it  were  visible,  as  it  is  not,  would  look  something  like  the  picture.  Such 
waves  go  out  from  a  sounding  bell  in  every  direction.  When  they  come  to  your  ear  you 
hear  the  bell,  but  not  before.  Sound  waves  travel  about  noo  feet  in  a  second  —  a 
mile  in  about  five  seconds. 

unless  there  were  some  person  to  hear  it.  If  there  were  a 
mechanical  piano  playing  at  the  north  pole,  by  machinery, 
there  would  be  vibration  of  the  strings  —  and  of  the  air,  too ; 
but  unless  there  were  some  one  to  hear  it  there  would  be  no 
sound,  only  vibration. 

Tom.    Well,  usually  there  are  persons  to  hear  in  our  part  of 
the  world.     Are  all  the  sounds  we  hear  caused  by  vibrations  ? 


PHYSICS  113 

Musical  Instruments.  — Jack.  Yes  ;  let  us  take  some  sounds 
we  know  about  and  see  what  makes  them.  In  the  first  place 
there  is  the  bell.  The  hammer  strikes  it  and  makes  it  vibrate. 
It  is  just  the  same  with  a  piano  ;  the  wire  is  struck  and  made 
to  vibrate.  A  violin  string  vibrates.  In  an  organ  pipe  or  in  a 


FIG.  94 

A  glass  plate  vibrates  when  a  fiddle  bow  is  drawn  across  its  edge  so  that  the  plate  makes  a 
sound.  If  you  put  a  little  clean  dry  sand  on  the  plate,  the  sand  will  move  so  as  to  make 
patterns  (as  in  the  cut).  By  drawing  the  bow  at  different  places  you  can  get  different 
patterns,  especially  if  you  lightly  touch  the  plate  with  a  lead  pencil  while  the  bow  is 
moving.  Some  of  the  patterns  are  shown  in  the  next  picture. 

trumpet  the  air  vibrates.  When  you  speak  or  sing  a  couple  of 
elastic  muscles  in  your  throat  vibrate.  In  a  drum  the  parchment 
vibrates  when  the  drumsticks  strike.  Something  always  vibrates 
first ;  that,  whatever  it  is,  sets  the  air  to  vibrating,  and  the 
vibration  travels  to  where  we  happen  to  be  and  we  hear  a  sound. 


THE  SCIENCES 


Tom.    How  do  you  know  that  the  bell  vibrates  ? 
Jack.    The  next  time  you  are  in  the  village  go  up  in  the 
clock  tower  when  the  clock  is  going  to  strike  and  hold  a  lead 
pencil  against  the  bell.     You  can/^/  the  bell  vibrate. 

Here  is  a  curious  thing  to  think  of.     First  the  bell  vibrates 
and   you    can   hear  it    for    miles    in    every  direction.     Every 


\ 


V — ' 


•*{•£***• 


FIG.  95.     PATTERNS  MADE  BY  LOOSE  SAND  ON  A  VIBRATING 
PLATE.     (SEE  FIG.  94.) 

After  the  patterns  have  been  made  they  can  be  preserved  by  carefully  pouring  varnish 
on  the  plate  and  letting  it  dry. 

particle  in  a  very  large  sphere  of  air  is  set  in  motion.  We 
hear  the  sound  at  our  house,  miles  away  from  the  village.  Now 
the  air  that  is  set  in  motion  weighs  hundreds  of  tons,  and  it  is 
all  moved  by  one  stroke  of  the  hammer  on  the  bell. 


PHYSICS  115 

Tom.    You  can  hear  a  locust  chirping  a  quarter  of  a  mile  off. 
I  suppose  he  sets  the  whole  air  in  motion,  too. 

Jack.  That  is  a  very  good  example.  A  small  insect  moves  tons 
and  tons  of  air ;  and  a  violin  string,  vibrating  so  little  that  you 
can  hardly  see  it  move,  stirs  all  the  air  in  a  great  concert  hall. 


FIG.  96 

A  watch  ticking  in  front  of  one  mirror  can  be  plainly  heard  through  a  tube  placed  in  front 
of  another.  If  you  take  the  second  mirror  away,  you  cannot  hear  it  at  all.  The  first 
mirror  acts  as  a  speaking  trumpet  (a  megaphone),  and  the  second  mirror  acts  as  an  ear 
trumpet. 

Sometimes  when  the  organ  is  playing  a  low  note  in  church 
you  can  actually  hear  the  air  flutter  and  vibrate.  The  organ 
makes  a  noise  then,  not  music. 

Mary.    What  is  the  difference  between  noise  and  music,  Jack  ? 


Il6  THE  SCIENCES 

Jack.  If  the  vibrations  of  a  bell,  a  violin  string,  an  organ 
pipe  —  anything  —  come  at  even  intervals,  then  they  make  a 
musical  note.  If  they  come  irregularly,  the  sound  is  usually  a 


FIG.  97.     ECHOES 

An  echo  is  made  by  the  reflection  of  sound  from  a  wall,  a  rock,  etc.     The  person  who 
speaks  must  be  at  least  100  feet  away  from  the  wall  to  get  a  good  echo. 

mere  noise.     Music  is  pleasant  to  hear,  and  noise  is  not.     That 
is  the  real  difference. 

Reflection  of  Sound.  —  Sound  can  be  reflected  somewhat  as 
light  is,  as  the  following  experiment  shows. 
Musical  Notes. — Mary.  Are  the  sounds  from  my  piano  regular? 
Jack.    Yes  ;    perfectly  regular.     Each  string  vibrates  regu- 
larly just  so  many  times  in  a  second,  no  more  and  no  less.     The 
middle  C  of  your  piano  is  a  wire  just  long  enough 
to  vibrate  261  times  every  second,  and  all  of  its 
vibrations  are  alike. 
The  shorter  a  string  is  the  quicker  it  vibrates,  and  you  will 
notice    that  the  highest  notes  of  your  piano  come  from  the 


PHYSICS  1 1 7 

shortest  strings.     It  is  the  same  with  drums ;  the  small  drums 
give  the  highest  notes,  the  large  drums  the  lowest. 

The  phonograph  is  a  machine  for  recording  the  vibrations  of 
the  air  that  are  made  when  a  person  speaks.  He  speaks  into 
a  tube  (F  in  Fig.  98)  and  sets  the  air  into  vibration.  At 
the  small  end  of  the  tube  is  a  little  round  thin  metal  plate  that 
moves  up  and  down  (slightly)  as  the  air  vibrates.  The  motions 
of  this  little  plate  copy  the  vibrations  of  the  air.  On  the  lower 
side  of  this  thin  plate  is  a  sharp  needle  point.  (See  Fig.  99.) 


FIG.  98.     THE  PHONOGRAPH 

While  the  person  is  speaking  the  barrel  (A),  which  is  covered 
with  tin  foil,  is  turned  by  the  crank,  and  the  little  needle  makes 
marks  on  the  tin  foil.  These  marks  are  the  record  of  the 
human  voice.  Every  vibration  of  the  voice  has  left  its  mark 
on  the  tin  foil.  If  now  we  put  a  piece  of  tin  foil  so  marked 
into  the  machine  and  turn  the  barrel,  what  will  happen  ?  As 
each  one  of  the  marks  in  the  tin  foil  passes  underneath  the  small 
needle  the  needle  will  move  a  little  (if  the  mark  in  the  tin  foil  is 
shallow)  or  moves  a  little  more  (if  the  mark  in  the  tin  foil  is 
deep).  The  needle  will  move  up  and  down  for  the  tin  foil  just 
as  it  formerly  moved  up  and  down  for  the  voice.  As  the 


Il8  THE  SCIENCES 

needle  moves,  so  must  the  thin  plate  move  ;  and  as  the  plate 
moves  and  vibrates,  so  must  the  air  above  it  move  and  vibrate, 
and  you  will  hear  from  the  machine  riow  the  very  words  you 
spoke  into  it  an  hour  ago,  or  a  year  ago,  or  twenty  years  ago, 
whenever  the  record  on  the  tin  foil  was  made.  You  can  keep 
the  tin  foil  and  repeat  the  words  whenever  and  wherever  you  like. 
Tom.  If  the  phonograph  had  been  invented  in  Julius  Caesar's 
time,  we  might  be  able  to  hear  his  voice  now,  or  George  Wash- 
ington's, or  Lincoln's. 

Jack.    The  records  of  the  speeches 
of  some  of  the  great  men  of  to-day 
actually   have   been    preserved ;   and 
long  after  they  are  dead,  so  long  as  the 
FlG  little  pieces  of  tin  foil  last,  other  peo- 

ple will  know  exactly  how  they  spoke. 
Mary.    It  would  be  a  fine  thing  for  us  to  get  Eleanor  to  sing 
into  a  phonograph  now,  so  that  when  we  go  home  after  vaca- 
tion we  could  still  hear  her  ! 

Jack.  A  wise  man  in  England l  once  suggested  that  there 
could  be  no  worse  punishment  in  a  future  life  than  to  be  forced 
perpetually  to  hear  all  the  foolish  things  you  had  said  in  this 
life.  It  might  not  be  a  bad  way  to  punish  naughty  boys  and 
girls  in  this  world  to  shut  them  up  in  a  room  with  phonographs 
that  would  continually  repeat  the  silly  and  foolish  things  they 
had  said. 

Agnes,  /think  it  would  be  dreadful,  Jack.  Nothing  could 
be  worse. 

Jack.  Very  well,  my  dear,  you  need  not  mind.  The  things 
you  say  are  always  nice  to  hear.  I  was  only  trying  to  frighten 
the  boys. 

1  Charles  Babbage  (born  1792,  died  1871). 


PHYSICS  119 

ELECTRICITY 

The  children  made  some  experiments  in  electricity  which 
any  one  of  you  can  make  too,  if  you  like.  You  will  need  a  few 
things,  most  of  which  you  can  get  at  home  or  make  for  your- 
self. A  few  you  will  have  to  buy  (they  do  not  cost  much). 
The  principal  things  to  get  are  :  a  couple  of  toy  magnets,  one 
straight,  one  shaped  like  a  horseshoe ;  a  piece  of  glass  tube 
(or  a  glass  rod)  about  half  an  inch  in  diameter  and  eight  or  ten 
inches  long ;  a  piece  of  sealing  wax  about  half  an  inch  square 


Copper 


wire 


Zinc 

B 

wire 

FIG.  100 

and  about  six  inches  long ;  a  rubber  comb  ;  an  old  silk  hand- 
kerchief ;  a  piece  of  old  flannel ;  an  ounce  of  sulphuric  acid  in 
a  bottle  with  a  glass  stopper  (be  careful  not  to  get  the  acid  on 
your  hands,  and  be  sure  that  the  bottle  is  labeled  Sulphuric 
Acid} ;  an  ounce  of  quicksilver  in  a  bottle  (be  sure  that  the 
quicksilver  is  labeled  ;  it  is  poisonous  if  swallowed) ;  about 
twenty  feet  or  so  of  insulated  copper  wire  (No.  18  annunciator 
wire  is  the  most  handy  to  use) ;  a  piece  of  sheet  copper  about 
three  sixteenths  of  an  inch  thick,  one  and  one  half  inches  wide, 
and  five  inches  long;  a  piece  of  sheet  zinc  of  the  same  size  as 
the  copper.  Take  the  copper  sheet  and  the  zinc  sheet  to  a 
plumber  and  have  him  solder  a  piece  of  copper  wire  (each 
piece  about  twelve  inches  long)  at  A  and  B.  After  this  is  done 


120  THE  SCIENCES 

take  a  large  tumbler,  fill  it  two-thirds  full  of  water,  pour 
three  tablespoonfuls  of  sulphuric  acid  in  it  (use  an  old  kitchen 
spoon  for  this  purpose),  dip  the  zinc  plate  in  it,  and  leave  it 
there  for  a  minute.  Then  take  the  zinc  plate  out,  hold  it 
over  a  china  plate,  pour  quicksilver  on  it,  and  rub  the  quick- 
silver on  to  the  surface  of  the  zinc  until  it  is  all  covered  and 
shining.  (Do  not  empty  the  water  and  acid  from  the  tumbler ; 
you  will  need  it  by  and  by ;  save  it.)  Now  you  have  all  the 

things  you  need  for  your  experi- 
ments, but  it  is  convenient  to  get 
two  dottble  connectors  (so  called) 
FIG.  ioi  like  Fig.  101. 

A  double  connector  (so  called)  is  a  cylinder  Jack.     Before     WC     begin     Our 

of  brass  with  two  holes  in  it  and  with      experiments  with  the  things  you 

two  screws.     It  is  used  to  connect  the  °     J 

ends  of  two  wires  and  saves  the  trouble        have  Collected,  tell  me  what  yOU 

of  twisting  the  ends  together,    it  is      already  know  about  electricity. 

convenient,  though  not  necessary. 

You  have  heard  it  talked  about. 
Tell  me  what  you  have  seen  on  your  own  account. 

Agnes.    Well,  lightning  is  electricity,  they  say. 

Mary.  And  electric  bells  ring  by  electricity,  and  some  street 
railways  go  by  electricity. 

Fred.    And  then  there  is  the  electric  telegraph. 

Tom.    Yes,  and  the  telephone,  and  the  electric  light. 

Jack.  All  these  things  have  to  do  with  electricity.  Let  us 
begin  by  making  some  lightning. 

Agnes.    Oh,  Jack  !  make  lightning?     It  would  be  dangerous. 

Tom.  Agnes  thinks  Jack  can  make  anything — even  a 
thunderstorm  if  he  wants  to. 

Jack.  Well,  Agnes,  the  lightning  we  are  going  to  make  will 
not  be  dangerous  ;  but  I  will  put  off  making  it  for  a  little  while 
and  begin  with  something  else. 


PHYSICS 


121 


Here  is  a  lot  of  small  pieces  of  tissue  paper  —  they  are 
very  light,  you  see  —  laid  on  the  table.  Now  take  the  glass 
rod,  Agnes,  and  hold  it  over  them.  What  happens? 


FIG.  102 

Little  pieces  of  tissue  paper  (or  light  grains  of  sawdust)  are  attracted  by  a  glass  rod  rubbed  with 
.  a  silk  handkerchief  (or  by  a  piece  of  sealing  wax  or  a  rubber  comb  rubbed  with  flannel). 

Agnes.    Nothing  happens  at  all. 

Jack.    Try  the  rubber  comb,  Mary. 

Mary.    Well,  nothing  happens. 

Jack.  Now,  Agnes,  rub  the  glass  rod  briskly  with  the  silk 
handkerchief  ;  and  you,  Mary,  rub  the  comb  with  the  flannel ; 
and  try  again  ;  Agnes  first. 

Agnes.  Why,  Jack!  the  little  pieces  of  paper  rise  up  to  meet 
the  glass.  (See  Fig.  102.) 

Jack.  Take  the  glass  rod  away,  Agnes  ;  and  now,  Mary,  try 
with  your  comb. 


122  THE   SCIENCES 

Mary.  It  is  just  the  same  thing;  the  little  pieces  of  paper 
rise  up  to  meet  the  comb  —  it  is  like  magic. 

Jack.  We  have  learned  something,  anyway.  What  have  we 
learned,  Fred,  so  far  ? 

Fred.  We  have  learned  that  if  you  rub  a  glass  rod  with  silk, 
the  rod  will  attract  pieces  of  paper  as  a  magnet  attracts  pieces 
of  iron. 

Tom.  And  that  if  you  rub  a  piece  of  rubber1  with  flannel, 
the  same  thing  happens. 

Jack.  That  is  very  good  so  far.  Now,  Agnes,  rub  the  glass 
rod  with  the  flannel,  not  the  silk ;  and  Mary,  rub  the  comb 2 
with  the  silk,  and  both  of  you  try  once  more.  What 
happens  ? 

Agnes.    Nothing  happens  now. 

Mary.    Nothing  happens  when  I  try  with  the  comb  either. 

Jack.  Well,  we  have  learned  that  to  lift  the  little  pieces  of 
paper  with  a  glass  rod  you  must  rub  the  rod  with  silk,  not 
flannel ;  and  the  comb  with  flannel,  not  silk.  Glass  rubbed 
with  silk  is  made  electric  —  electrified,  as  they  call  it ;  and 
rubber  (or  sealing  wax)  rubbed  with  flannel  is  electrified. 
When  either  glass  or  rubber  is  so  electrified  it  will  attract 
little  pieces  of  paper,  or  light  grains  of  sawdust. 

I  want  you  all  to  try  this  experiment,  too.  Electrify  the 
glass  rod  and  the  comb  and  then  hold  them  near  your  face. 
What  happens  ? 

Agnes.  Why  it  tickles !  it  feels  as  if  there  were  a  cobweb  on 
my  cheek. 

1  A  piece  of  sealing  wax  rubbed  with  flannel  will  act  just  as  the  rubber  comb 
acts.     Try  it. 

2  A  piece  of  amber  does  the  same  thing.     The  Greek  name  for  amber  is  elek- 
tron,  and  we  get  the  name  "  electricity  "  that  way. 


PHYSICS  123 

Jack.  Tom,  take  the  glass  rod  and  rub  it  smartly  with  the 
silk.  Now  hold  your  knuckle  close  down  to  the  tube.  See 
there  is  a  little  spark. 

Tom.    I  felt  it  and  I  heard  it,  too. 

Jack.  Agnes,  that  spark  was  lightning  and  the  crackling 
noise  was  thunder,  only  they  are  not  dangerous.  Real  light- 
ning is  just  the  same  kind  of  thing  as  that  little  spark, -and 
real  thunder  is  just  like  the  little  noise  the  spark  made.  Per- 
haps you  know  that  in  1752  Benjamin  Franklin  sent  a  kite  up 
in  the  air  during  a  thunderstorm  and  brought  down  some  of 


FIG.  103.     A  LONG  ELECTRIC  SPARK  BETWEEN  Two  ELECTRIFIED  BALLS 

Lightning  takes  the  shape  of  this  spark.    It  is  never  a  zigzag  bolt  made  up  of 
straight  lines,  as  it  often  seems  to  be. 


the  electricity  that  was  in  the  clouds  and  proved  that  the  light- 
ning in  the  sky  was  exactly  the  same  thing  as  the  spark  you 
have  just  seen. 

Now  you  children  have  seen  the  kind  of  electricity  that 
makes  thunder  and  lightning.  Let  us  make  some  of  the  kind 
that  they  use  in  the  telegraph.  I  want  to  make  a  current  of 
electricity  that  I  can  use  to  carry  a  message  from  New  York 
to  San  Francisco. 

Now  we  shall  need  our  tumbler  of  water  with  the  acid  in  it 
and  the  strips  of  copper  and  zinc.  (See  page  119.)  Stand  the 


I24 


THE  SCIENCES 


two  strips  upright  in  the  tumbler  and  put  some  strips  of  wood 
across  the  top  of  the  tumbler  to  keep  the  zinc  and  copper  apart. 
They  must  not  touch  anywhere.  When  you  have  arranged  this 
all  right  so  that  everything  will  stay  in  place  you  have  got  a 
battery,  and  if  you  join  the  two  wires  (see  the  picture,  Fig.  104) 

a  current  of  electricity  will  flow 
from  the  copper  plate  to  the 
zinc.  I  am  going  to  prove  it 
to  you. 

Take  the  end  of  the  wire 
from  the  copper  and  put  it  on 
one  side  of  your  tongue  and 
put  the  wire  from  the  zinc  on 
the  other  side,  and  you  '11  feel 
a  little  current  passing.  The 
current  goes  from  the  copper 
through  the  wire,  and  through 


A  glass  jar  containing  dilute  sulphuric  acid 
with  a  plate  of  zinc  and  a  plate  of  copper 


your  tongue  to  the  zinc.    Your 
tongue  connects  the  two  wires. 

in  it  (they  must  not  touch  each  other)  is      Jf    vou     actually    join    the    two 

called  an  electric  battery.      If  you  join 

the  coppar  (C)  and  the  zinc  (Z)  plates  by 

a  wire  (Af),  a  current  of  electricity  will 

flow  from  C  to  Z  through  the  wire;   no 

matter  how  long  the  wire  is,  the  current 

will   still   flow.      It  would   flow  (with  a 


wires,  the  current  will  be  there 
just  the  same.  Feeling  it  with 
your  tongue  proves  that  it  is 
there,  and  that  is  what  I  wanted 


strong  current)  from  New  York  to  Boston.      j.Q  prove        Jf  yOU 

batteries  joined  together,1  you  would  have  a  current  twice  as 
strong.  With  many  batteries  joined  together  you  would  have 
a  current  strong  enough  to  travel  over  a  wire  as  long  as  from 
New  York  to  Boston ;  and  that  is  the  kind  of  electricity  they 
use  in  telegraphing. 

1  The  zinc  of  one  battery  to  the  zinc  of  the  next  one. 


PHYSICS 


The  Telegraph.  —  "I  understand  how  you  send  a  current  of 
electricity  from  New  York  to  Boston,"  said  Tom  ;   "you  have  a 


FIG.  105.     A  BATTERY  OF  FIFTEEN  CUPS 

Notice  that  the  zinc  qf  one  cup  is  connected  to  the  copper  of  the  next  one,  and  so  on. 
At  the  ends  there  are  two  short  wires  marked  +  and  — .  If  you  join  these  to  two 
telegraph  wires  reaching  to  a  distant  town,  a  current  of  electricity  will  flow  from  +  to 
the  distant  town  and  back  from  the  town  to  — .  There  would  be  a  continuous  circuit 
of  wire  from  +  to  the  town,  and  back  again  to  — .  If  you  cut  the  circuit  of  wire  any- 
where and  put  the  two  ends  of  the  wire  to  your  tongue,  you  will  feel  the  current. 
That  is  a  proof  that  the  current  is  always  there,  in  the  wire.  It  is  always  flowing  so 
long  as  the  battery  is  joined  to  the  long  loop,  or  circuit  of  wire. 

battery  at  New  York  and  a  loop  of  wire  —  what  you  call  a  cir- 
cuit —  going  to  Boston  and  returning  to  New  York,  this  way : 

wire  ^ 


Battery  in 
New   York 


Boston 


wire 
FIG.  1 06 


126  THE   SCIENCES 

But  I  don't  see  how  you  make  the  signals.  The  current  flows 
through  the  wires  quietly ;  it  makes  no  noise." 

Fred.  You  have  to  put  telegraph  instruments  —  a  key  and  so 
forth  —  on  the  wire,  don't  you  ? 

Jack.  Yes  ;  we  can  improve  Tom's  drawing  by  putting  them 
in,  this  way  : 


wire 


Battery  in 
New,  York 

Telegraph  Instrument 

Telegraph  Instrument  in  Boston 

in  New  York 


< wire 

FIG.  107 

The  battery  in  New  York  is  all  the  while  sending  a  current 
of  electricity  along  the  wire.  It  fills  the  whole  of  the  wire 
from  New  York  to  Boston  and  back  again.  It  flows  along 
the  wire  and  through  the  telegraph  instruments  at  both  places. 
When  you  wish  to  talk  to  Boston  you  move  your  New  York  key 
up  and  down,  and  the  receiving  instrument  in  Boston  makes 
little  sounds,  one  sound  for  each  motion  of  the  New  York  key. 
You  can  arrange  an  alphabet  that  way.  For  instance,  three  dots 

( )  might  be  C,  one  dot  (-)  might  be  E,  and  two  dots  (-  -)  might 

be  /.  You  could  spell  .ice,  for  example,  this  way  :  -  -, ,  - . 

Fred.  And  Boston  could  talk  to  New  York  by  dotting  with 
the  Boston  key,  and  New  York  would  hear  it. 

Jack.  That  is  exactly  the  way  it  is  done.  Go  into  a  tel- 
egraph office  sometime  and  listen,  and  you  will  hear  the 
instruments  clicking  away.  Sometimes  they  make  dots  and 


PHYSICS 


127 


FIG.  108 

This  figure  shows  the  way  in  which  New  York  and  Boston  are  connected  by  telegraph. 
It  is  more  complicated  than  the  way  described  before,  but  the  idea  is  the  same. 
The  key  at  New  York  is  marked  K  (the  Kon  the  right-hand  side) .  If  this  key  is  tapped, 
a  signal  goes  over  the  wire  to  Boston  and  is  received  on  a  sounder  there.  (See  the  picture 
of  the  sounder  at  the  bottom  of  the  cut.)  In  the  same  way  signals  made  with  the 
Boston  key  are  heard  on  the  New  York  sounder. 

sometimes  longer  sounds   called  dashes,  and   sometimes  very 
long  dashes.     The  alphabet  they  use  is : 

TELEGRAPHIC  ALPHABET 


A 

B 

C 

D 

E 

F 

G 

H 

I 

J 

K 

L 

M 

N 

O 

P 

Q 

R 

S 

T 

u 

V 

W 

X 

Y 

Z 

& 

t 

p 

TELEGRAPHIC 

FIGURES 

( 

i 

2 

3 

4 

5 

6 

7 

8 

9 

10 

FIG.  109 


128 


THE   SCIENCES 


Velocity  of  Electricity.  —  "  You  children  must  remember,"  said 
Jack,  "that  electricity  travels  at  the  same  speed  as  light  —  it 
travels  186,000  miles  in  a  second.  They  once  sent  a  message 
from  Cambridge  through  Canada  to  San  Francisco,  returning 
by  Omaha  and  Chicago,  and  it  took  only  four  seconds  for  the 

message  to  go  those 
7000  miles.  If  the  tele- 
graph instruments  had 
been  perfect,  the  mes- 
sage would  have  gone 
instantaneously.  As  it 
was  it  did  not  take  long." 

MAGNETISM 

Jack.  Suppose  we  stop 
talking  about  electricity 
for  a  while  and  learn 
something  about  mag- 
nets. There  is  a  magnet 
in  every  telegraph 
sounder,  in  every  tele- 
phone, and  in  every 
dynamo,  and  I  want  you 

to  understand  how  they  are    used.     But  we  will  begin  far  off 

and  come  to  these  complicated  machines  by  and  by.     In  the 

first  place,  Fred,  what  is  a  magnet  ? 

Fred.    A  magnet  is  a  piece  of  iron  or  steel  that  attracts  other 

pieces  of  iron. 

Tom.    Try    your    straight    magnet    on    these    iron    filings, 

Fred. 


FIG.  no 


A  straight  magnet  held  in  the  hand  will  attract  little 
pieces  of  iron  and  will  make  each  of  them  into  mag- 
nets, so  that  they  will  hold  up  other  small  pieces. 


PHYSICS 


129 


Jack.  There  is  a  special  thing  to  notice.  A  bar  magnet 
attracts  iron  filings,  tacks,  and  so  forth,  at  its  ends,  but  not  at 
its  middle.  It  is  just  the  same 
with  a  horseshoe  magnet.  Try  it. 

We    have    learned    one    thing. 
Magnets  of  all  shapes  attract  iron 

filings,  tacks,  needles,  and  SO  forth,      A  straight  magnet  — a  bar  me 

to  their  ends,  not  to  their  centers.       attracts  iron  filinss  to  its  ends> but 

,,  ,  ..     .          .,  ,  not  to  its  middle  part. 

Here  are  four  little  piles  of  saw- 
dust, of  copper  filings,  of  sand,  and  of  coal  dust.     Try  to  pick 

them  up  with  your  magnets. 

Agnes.   They  do  not  move  ;  magnets 
do  not  attract  such  things  as  sand. 
Jack.       No; 


FIG.  in 


FIG.  112 


magnets    attract 
iron  and  steel 

nothing  else. 

you    take     a 


A  horseshoe  magnet  attracts  iron 
filings  to  its  ends;  but  if  you 
try  the  curved  part  of  the  mag- 

net  on  a  needle,  there  is  almost      pile    of    CODDer 
no  attraction. 

filings    and  iron 

filings  mixed  together,  the  magnet  will 
pick  up  the  iron  filings  and  leave  the 
copper.  Try  the  experiment  and  see  for 
yourself. 

Tom.    So  it  does.      That  is   a  way   of  FlG-  "3-    A  HORSESHOE 

,r  MAGNET  WITH  AN  IRON 

sorting  iron  out  of  a  pile.     If  some  one     BAR    (AN    ARMATURE) 
told  me  to  pick   the   iron   filings   out   of      ACROSS  ITS  ENDS 
this  pile  by  hand,  it  would  take  all  day 

to   do   it ;   but   with   a   magnet    I   can   do   it   in   five  minutes. 

Jack.    See    what    the    magnet    will    do    through    a    pane   of 

glass.     Lay  a  needle  on  a  pane  of  glass  held  horizontally  and 


130 


THE  SCIENCES 


put  the  magnet  under  the  glass.     You  will  see  that  the  needle 
moves  over  the  glass  as  you  move  the  magnet  around. 
Tom.    So  it  does ;  glass  does  not  stop  the  attraction. 
Jack.    Try  putting  the  needle  on  a  sheet  of  writing  paper  or 
on  a  piece  of  silk. 

Tom.    It  is  just  the  same;  the  needle  moves  when  I  move 
the  magnet. 

Jack.    So  much  is  clear  ;  a  magnet  is  made  of  iron;  it  attracts 
iron  and  nothing  else;  it  attracts  it  through  silk,  or  paper, 

or  glass  —  through  any- 
thing. 

These  magnets  that 
you  have  been  using 
are  manufactured. 
They  were  made.  Let 
us  make  some  more. 
Agnes,  have  you  got 
any  needles  ? 

Agnes.  Here  are  some. 
Jack  laid  the  needles 
on  the  table  and  rubbed 
them  with  the  horseshoe 
magnet,  as  if  he  were 
stroking  them  with  it.1 
He  tried  each  needle  on 
the  pile  of  iron  filings, 
and  every  one  was  able  to  lift  up  some  filings  just  as  the  horse- 
shoe magnet  did.  Then  he  took  two  of  the  needles  and  tied  a 
bit  of  silk  about  each,  near  its  middle,  and  hung  the  silk  from 

1  Make  all  the  strokes  on  all  the  needles  in  one  direction,  so  as  to  have  the  needle 
magnets  all  alike.    Stroke  all  of  them  from  eye  end  to  point,  or  all  from  point  to  eye. 


FIG.  114 

Iron  filings  on  a  horizontal  pane  of  glass  will  move 
into  a  certain  set  of  curves  when  yon  hold  a  horse- 
shoe magnet  underneath  the  glass.  (You  must 
tap  the  glass  very  gently  with  your  finger  tip.) 


PHYSICS 


two  pencils  (see  Fig.  115),  so  that  he  had  two  little  magnets, 
like  pendulums.  Next  he  took  the  bar  magnet  —  a  straight 
magnet  —  and  tried  some  experiments  with  needle  No.  i  (the 
other  needle  was  laid  aside  for  the  moment).  The  bar  magnet 

pencil  ^••^•i  -—^—tp—— pencil 


silk 


needle 
no.  i 


silk 


needle 
no.  2 


FIG.  115 


had  two  ends  of  course ;  one  was  the  point,   and   the  other 
happened  to  be  painted  red. 


point 


red 


FIG.  116 


By  trials  with  needle  No.  i  he  found  : 

1.  That  the  point  of  the  bar  magnet  attracted  the  point  end 
of  needle  No.  i. 

2.  That  the  point  of  the  bar  magnet  repelled  the  eye  end  of 
needle  No.  i. 

3.  That  the  red  end  of  the  bar  magnet  repelled  the  point 
end  of  needle  No.  i. 

4.  That  the  red  end  of  the  bar  magnet  attracted  the  eye  end 
of  needle  No.  i. 

Then  he  tried  needle  No.  2  and  found  just  the  same  things 
for  it  also. 


132  THE  SCIENCES 

5.  The  point  of  the  bar  magnet  attracted  the  point  end  of 
needle  No.  2  ; 

6.  — and  repelled  the  eye  end  of  No.  2. 

7.  The  red  end  of  the  bar  magnet  repelled  the  point  end 
of  No.  2 ; 

8.  •  —and  attracted  the  eye  end  of  No.  2. 

The  next  thing  was  to  put  aside  the  bar  magnet  and  to  try 
the  two  needles  together.  He  found  : 

9.  That  the  two  points  of  the  needles  repelled  each  other. 

10.  That  their  two  eye  ends  repelled  each  other. 

11.  and  12.    That  the  point  end  of  either  needle  attracted  the 
eye  end  of  the  other.1 

Tom.  What  is  the  explanation  of  all  these  experiments, 
Jack  ? 

Jack.  It  is  like  this  :  just  suppose  there  were  two  kinds  of 
magnetism  in  the  bar  magnet.  We  might  call  them  point-end 
magnetism  and  red-end  magnetism,  for  want  of  better  names. 
Now  when  we  made  magnets  out  of  these  needles  we  put  the 
two  kinds  of  magnetism  into  them.  We  put  one  kind  into  the 
point  ends  of  both  needles  and  another  kind  into  their  eye 
ends.  Suppose  we  say  that  point-end  magnetism,  where- 
ever  it  is  found,  will  repel  point-end  magnetism  ;  and  that 
red-end  magnetism,  wherever  found,  will  repel  red-end  mag- 
netism ;  and  that  point-end  magnetism  will  attract  red-end 
magnetism,  and  vice  versa,  wherever  they  are  found.  Would  not 
that  explain  all  that  we  have  seen  ? 

Taking  all  the  twelve  cases  one  by  one,  the  children  found 
that  the  explanation  was  right.  Magnetism  of  the  same  name 
repels  ;  magnetism  of  different  name  attracts.  It  is  not  easy 

1  These  experiments  take  some  space  to  describe,  but  they  are  so  interesting 
that  they  should  be  tried  in  the  schoolroom. 


PHYSICS 


133 


to  explain  in  simple  words  why  this  is  so ;  but  any  child  who 
will  pay  attention  and  make  these  simple  experiments  can 
prove  it. 

Natural  Magnets.  —  "These  magnets  were  artificial;  they 
were  manufactured,"  said  Jack  ;  "but  there  are  stones  that  are 
magnetic  to  begin  with.  They  were  first  found  in  Magnesia, 
a  town  of  Asia  Minor,  long  ago,  and  the 
ancients  therefore  called  them  magnets." 

Mary.  In  the  Arabian  Nights,  in  "  Sind- 
bad  the  Sailor,"  there  is  a  story  of  a  whole 
mountain  made  of  magnets,  so  that  when 
a  ship  came  that  way  the  mountain  pulled 
all  its  iron  nails  out,  and  the  ship  broke  to 
pieces  and  sank. 

Agnes.    That  is  n't  true,  is  it  Jack  ? 

Jack.  Certainly  not,  my  dear ;  it  is  one 
of  the  big  stories  told  by  travelers.  But 
don't  you  recollect  how  they  got  past  the 
mountain  with  their  ships  ? 

Mary.  They  built  their  ships  with  wooden 
pins  instead  of  nails  and  got  safely  past, 
so  the  story  says. 

Electro-Magnets. — Jack.  There  is  an- 
other kind  of  magnet  that  I  want  you  to  know  about.  It  is 
made  by  a  current  of  electricity  from  a  battery  passing  through 
a  wire  wrapped  round  a  bar  of  soft  iron.  (See  Fig.  1 17.) 

You  see  now  how  a  telegraph  operator  in  New  York 
can  make  a  click  on  the  sounder  in  Boston.  The  bat- 
tery current  is  flowing  all  the  time  except  just  at  the 
moment  when  the  New  York  man  lifts  his  key  and  breaks 
the  circuit. 


FIG.  117 

If  wire  be  wrapped  in  a 
spiral  around  a  bar  of 
iron,  and  if  a  current  of 
electricity  flow  through 
the  wire,  the  bar  be- 
comes a  magnet  and 
stays  so  as  long  as  the 
current  is  flowing,  and 
no  longer. 


134 


THE  SCIENCES 


The  electro-magnet  of  the  sounder  in  Boston  is  a  magnet  so 
long   as    the    current   flows,   and    stops    being   a  magnet  the 


FIG.  118 

Electro-magnets  are  often  made  of  a  core  of  soft  iron  bent  into  the  shape  of  a  horseshoe, 
and  wound  with  wire.  The  two  ends  of  the  wire  go  to  the  copper  and  zinc  of  a  battery. 
So  long  as  the  current  flows  the  iron  core  is  a  magnet.  When  the  current  stops  it  is  no 
longer  a  magnet. 

instant  the  current  stops.  Whenever  the  New  York  man  lifts 
his  key  the  Boston  sounder  makes  a  click  —  a  dot  or  a  dash, 
just  as  he  chooses.  In  that  way  the  message  is  spelled  out. 


Key  in 
New  York 


Bai 


Sou  ider 
in  Boston 


tery 


FIG.  119 

Electric  Bells.  —  "Now,"  said  Jack,  "it  is  easy  to  understand 
how  electric  bells  work.  It  is  like  a  telegraph.  In  the  first  place 
you  must  have  a  battery.  We  could  make  a  battery  by  using 


PHYSICS 


135 


several  tumblers  (like  those  described  on  page  124),  but  it  is 
more  satisfactory  to  buy  one  cell  of  "dry  "battery,  so  called. 


FIG.  1 20.     A  TELEGRAPH  KEY 


FIG.  121.     A  REPEATING  SOUNDER 


FIG.  122.     A  CELL  OF 
DRY  BATTERY 

"  We  must  run  our 


The  coils  of  its  magnets  are  vertical.     Thearma-  wire     along     the    walls 

tare  is  fastened  to  the  horizontal  ter  which  from      one      station      to 
moves  as  the  armature  moves  and  clicks  against 

the  point  of  the  little  screw  above  it.  another    like    this  I  " 


wire 


Push 
Button 


Battery 


Bell 


wire 
FIG.  123 


FIG.  124.    A  PUSH  BUTTON 

It  is  like  a  very  simple  telegraph  key. 
When  you  push  it  two  ends  of  the  wire 
are  connected  so  that  the  current  from 
the  battery  can  flow  to  the  bell  and  ring 
it.  Until  the  button  is  pushed  the 
circuit  is  broken  and  the  current  can- 
not flow.  If  you  should  take  away 
the  push  button  and  join  the  ends  of 
the  wire  where  it  now  is,  the  battery 
current  would  flow  continuously  and 
the  bell  would  ring  all  the  time. 


FIG.  125.    AN  ELECTRIC  BELL 

When  the  push  button  is  touched  the  cur- 
rent from  the  battery  flows  along  the 
wire  into  the  box  and  round  the  coils 
shown  in  the  picture.  So  long  as  the 
current  is  flowing  the  soft  iron  inside 
the  coils  is  a  magnet  and  attracts  the 
piece  of  iron  which  is  -the  hammer  (K) 
of  the  bell  (T).  But  this  piece  is  a  vi- 
brating spring  and  it  keeps  moving  to  and 
fro  and  sounding  the  bell.  The  moment 
that  the  push  button  is  released  the  cur- 
rent stops  flowing  and  the  bell  stops 
sounding. 


136 


FIG.  126.     AN  ELECTRIC-BELL  OUTFIT 
COMPLETE 

It  can  be  bought  in  this  form  with  seventy-five 
feet  of  wire  and  staples  to  fasten  the  wire  for 
about  $2.75. 


Grou.ntL  Wire, 


Line  Wire. 


FIG.  127.     THE  TELEPHONE 

F  is  a  handle  ;  turn  it  and  the  bell  (G)  will  ring  on  your 
telephone  and  also  at  the  other  end  of  the  line.  The 
man  you  wish  to  talk  to  will  hear  it.  He  has  another 
instrument  just  like  yours.  Take  down  your  tele- 
phone (B)  and  put  it  to  your  ear.  Speak  into  your 
transmitter  (C)  and  he  will  hear  you  in  his  tele- 
phone. When  he  speaks  into  his  transmitter  you 
will  hear  him  in  your  telephone. 


to  Battery 


137 


138 


THE  SCIENCES 


The  Mariner's  Compass.  —  "You  know  that  a  magnetized 
needle  points  north  and  south,"  said  Jack.  "  A  compass  needle 
will  point  to  the  north  no  matter  to  what  part  of  the  earth  you 


FIG.  128.     THE  TELEPHONE 

One  view  shows  the  telephone  as  it  really  is ;  the  other  as  it  would  look  if  it  were  split  down 
the  middle  so  as  to  show  what  is  inside.  A  is  a  long  steel  magnet  wound  with  fine 
wire  (B).  The  ends  of  the  spool  of  wire  (B)  are  connected  to  the  outside  posts  (D,D). 
Close  to  the  magnet  yi(near  B)  there  is  a  thin  iron  plate  (EE)  which  vibrates  so  as  to 
copy  the  voice  of  the  person  speaking  to  you.  That  person  speaks  into  his  transmitter. 
(See  Fig.  127.)  The  vibrations  of  his  voice  make  vibrations  in  the  disk  of  his  trans- 
mitter ;  these  vibrations  are  sent  along  the  telephone  wire  and  come  to  your  telephone ; 
there  they  make  the  disk  (BE )  of  your  telephone  vibrate  just  ,as  his  voice  vibrated ; 
the  disk  (EE)  makes  the  air  in  your  telephone  vibrate  like  the  speaker's  voice,  and 
you  hear  him  speak. 

take  it.  The  reason  is  that  a  current  of  electricity  is  flowing 
round  and  round  the  earth  all  the  time  and  that  any  magnet 
will  always  arrange  itself  at  right  angles  to  a  current,  if  it  can. 


PHYSICS 


139 


The  fact  is  so,  and  I  am  going  to  prove  it."     So  Jack  took 
one    of   the    little   magnetized    needles   (Fig.  1 1 5)  and    let    it 


FIG.  129.     THE  MARINER'S  COMPASS 

swing    freely.      It    swung    so   as   to   point   to    the    north    and 
rested  in  that  direction,  thus : 


->•  North 


FIG.  130 

Then  Jack  took  the  two  ends  of  the  wire  from  his  battery 
and  made  them  parallel  to  the  needle,  being  careful  not  to 
touch  the  ends  together,  this  way: 

>  North 


AB 


Copper 


Zinc 

' 


Battery 
FIG.  131 


140  THE  SCIENCES 

No  current  was  flowing,  and  the  needle  remained  as  it  was 
before.  Then  he  joined  the  ends  A  and  B.  A  current  flowed 
through  the  wire,  and  immediately  the  needle  moved  round  and 
pointed  west  and  not  north  (Fig.  132). 

"You  see,"  said  Jack,  "the  needle  moves  so  as  to  be  perpen- 
dicular to  the  direction  of  the  current.  A  current  is  always 
flowing  round  and  round  the  earth  from  east  to  west.  The  sun 
makes  the  current.  The  compass  needle  is  always  perpendicular 
to  the  direction  of  the  current,  and  that  is  why  the  mariner's 
compass  points  to  the  north.  It  is  a  good  thing  for  us  that  it 

West 


Copp. 


er  Zinc 


Battery 
FIG.  132 

does  so.  Sailors  can  make  long  voyages  and  always  know 
which  way  is  north  whether  the  stars  are  shining  or  not. 
They  do  not  need  the  north  star  any  more." 

The  Electric  Light.  —  The  first  electric  light  was  made  about 
a  hundred  years  ago  by  using  a  battery  of  3000  cells.  (See 
Fig.  105.)  The  wires  from  the  ends  of  this  immense  battery 
were  brought  close  together,  and  the  spark  between  the  ends 
did  not  come  and  go  as  lightning  does,  but  was  steady,  like 
our  electric  , street  lamps.  The  current  from  so  many  cells 
made  a  great  heat  as  well  as  a  brilliant  light.  The  ends  of  the 
wires  were  melted  off  where  the  light  was  produced,  and  they 


o-w 

' 


H     -» 


. 


•SS'S'.SS3'; 


^rc  3  ^rc 

;s»*i 

S  3 ;  *  §  S 
«  °<S  o^e- 
6*8 


?! 


&B  ^ 


iF^EfiiB 
ss  ^Hffli 

„  ^H^  pjw'S1^  o  rt. 

l^eis.-^rg" 

lll'llslg^ 


— .     ^ 


"    0 


141 


142  THE  SCIENCES 

were  obliged  to  use  carbon  ends  (round  sticks  of  coal  dust  or 
coke)  at  the  ends,  just  as  we  do  to-day. 

The  Dynamo.  —  It  is  possible  to  make  batteries  of  thousands 
of  cells,  like  those  shown  in  Fig.  105,  so  powerful  as  to  do  the 
work  of  electric  lighting ;  but  it  is  very  troublesome  and 
expensive.  A  much  simpler  and  cheaper  way  to  get  the  current 
that  is  needed  is  to  use  a  dynamo  driven  by  a  steam  engine. 


FIG.  136.     A  DYNAMO-ELECTRIC  MACHINE 

A  belt  from  a  steam  engine  is  put  on  the  wheel  at  the  right  of  the  picture  and  turns  this 
wheel  very  rapidly.  The  central  part  of  the  dynamo  is  a  large  stationary  electro-magnet. 
Fastened  to  the  revolving  wheel  (and  not  visible  in  the  picture)  are  a  number  of  small 
electro-magnets.  When  these  small  electro-magnets  are  revolved  very  rapidly  in  front 
of  the  large  magnet  a  strong  current  of  electricity  is  made,  and  this  current  is  carried 
off  on  wires  to  where  we  wish  to  use  it.  It  will  light  lamps  or  drive  a  street  car,  etc. 

The  steam  engine  is  used  to  turn  a  set  of  little  electro- 
magnets in  front  of  a  larger  magnet.  When  this  is  done  a 
current  of  electricity  flows  through  two  wires  leading  from  the 
machine,  and  these  wires  can  be  led  to  the  place  where  we 
want  to  use  the  current  —  to  a  distant  part  of  the  city  to  light 


PHYSICS 


143 


lamps,  or  to  drive  electric  cars.     Lamps  are  lighted  by  letting 
the  current  from  the  dynamo  pass  through  them. 

Electric  Railways.  —  Street  cars  are  driven  in  this  way.    Under- 
neath each  car  is  a  dynamo  (called  a  motor}  fastened  to  the  wheels. 


FIG.  137.     PART  OF  THE  FRONT  TRUCK  OF  A  STREET  CAR  (SHOWING  THE 
WHEELS  AND  THE  MOTOR  BETWEEN  THEM) 


FIG.  138.     AN  ELECTRIC  STREET  RAILWAY 

The  power  house  with  its  dynamo  (D)  driven  by  a  large  steam  engine  is  shown  on  the  left- 
hand  side.  From  this  dynamo  a  current  goes  out  on  an  overhead  wire  (A*).  A  moving 
trolley  ( T)  on  each  car  takes  the  current  to  the  motor.  The  motor  turns  the  wheels 
whenever  the  motorman  turns  the  current  on,  and  stops  turning  them  whenever  he  shuts 
the  current  off. 


APPENDIX 


SOME  of  the  experiments  that  were  tried  by  the  children  are  given  here. 
Nearly  all  of  them  can  be  repeated  in  the  schoolroom  or  by  children  at 
home  who  will  take  the  trouble.  It  is  well  worth  while  to  do  it,  because 
we  learn  so  much  more  by  really  doing  a  thing  than  by  merely  talking  or 
reading  about  it.  The  teacher  can  readily  buy  or  make  the  simple  apparatus 
described  ;  and,  once  made,  it  will  serve  for  successive  classes.  Nearly 
every  child  has  a  father,  or  an  older  brother,  or  a  friend,  who  will  help  him 
to  make  these  experiments  at  home  if  they  cannot  be  seen  at  school. 

What  Kind  of  Things  Bodies  are. — We  need  a  convenient  name  for  solids, 
liquids,  and  gases  ;  let  us  call  them  bodies,  and  say  that  a  piece  of  iron  is 
a  solid  body,  a  lake  of  water  is  a  body  of  liquid,  etc.  When  we  think  about 
any  body  of  this  sort  —  a  nugget  of  gold,  for  instance  —  we  always  think  of 
it  as  filling  some  space. 

Extension.  —  All  bodies  are  extended;  they  fill  a  space.  Even  a  sponge 
fills  a  space ;  the  holes  in  the  sponge  are  full  of  air,  and  the  air  in  a  sponge 
fills  a  space  and  has  a  shape  of  its  own. 

Impenetrability.  —  Where  one  body  is,  another  body  cannot  be  at  the 
same  time.  Putty  is  soft  and  can  be  molded  into  almost  any  shape,  but 
where  the  putty  is,  nothing  else  can  be  at  the  same  time.  It  completely  fills 
its  own  space. 

Divisibility.  —  Every  body  can  be  divided  into  two  halves,  and  each  of 
those  halves  into  halves  again,  and  so  on.  If  you  will  get  from  the 
druggist  a  little  piece  of  permanganate  of  potash  (write  the  name  down) 
and  put  it  into  a  hogshead  of  water,  you  will  find  that  the  whole  of  the  water 
has  been  colored  red.  Every  drop  of  water  that  you  take  up  in  your  hand 
is  red,  and  there  are  millions  of  drops  in  the  hogshead.  That  means  that 
the  little  piece  of  permanganate  of  potash  has  been  divided  into  millions 
of  smaller  pieces,  and  that  every  single  drop  of  water  has  several  of 
those  small  pieces  in  it ;  for  it  takes  more  than  one  piece  to  color  a  whole 
drop  of  water. 

144 


PHYSICS  —  APPENDIX  1 45 

If  you  put  a  piece  of  musk  no  larger  than  a  green  pea  (you  can  buy 
musk  from  any  druggist)  in  a  room,  it  will  scent  the  room  and  everything 
in  it,  and  it  will  keep  on  doing  so  for  years  and  years.  Leave  a  towel  in 
the  room  over  night,  and  the  next  morning  every  thread  of  the  towel 
will  smell  of  musk.  You  could  go  on  leaving  towels  in  the  room  for  a 
dozen  years  and  taking  them  away  after  one  night,  and  every  thread  of 
every  towel  would  show  that  the  musk  had  been  near  it.  That  means  that 
every  one  of  the  threads  of  every  one  of  the  towels  has  several  particles  of 
musk  on  it ;  and  it  means  that  the  original  piece  of  musk  (which  seems 
hardly  to  grow  any  smaller)  has  been  divided  into  millions  of  little  pieces. 

Cohesion.  —  If  you  take  two  bars  of  soap  and  press  them  together  under 
a  press,  you  can  make  one  piece  out  of  the  two.  That  piece  is  held  together 
by  a  force  that  we  call  cohesion.  All  solids  are  held  together  by  such  a 
force.  One  part  of  a  lump  of  iron  is  held  to  the  other  parts  by  cohesion. 
It  requires  a  good  deal  of  pulling  to  pull  one  part  of  an  iron  rail  away  from 
the  other  parts  (though  it  can  be  done).  You  can  weld  two  pieces  of  iron 
together  (by  heating)  so  that  they  become  one  piece. 

If  you  stretch  a  solid  body  (or  compress  it)  and  then  take  away  the 
force  that  was  stretching  (or  pressing)  it,  the  body  will  usually  spring  back 
to  its  first  shape.  A  piece  of  india  rubber  stretched  (or  compressed)  flies 
back  to  its  first  shape  as  soon  as  you  stop  forcing  it  out  of  shape.  A 
bent  steel  knitting  needle  flies  back  into  shape  very  quickly.  India  rubber, 
steel,  glass,  and  indeed  most  solid  bodies,  are  elastic.  If  you  strain  them 
a  certain  amount,  they  will  spring  back  into  shape  like  the  springs  of  a 
buggy.  If  you  strain  them  too  much,  they  sometimes  lose  their  elasticity 
like  the  springs  of  a  farm  wagon  that  has  been  used  to  carry  very  heavy 
loads.  Most  solid  bodies  are  elastic;  all  liquids  are  so. 

Viscosity.  —  Did  you  ever  see  very  cold  molasses  flowing  from  a  spigot  ? 
It  is  viscous —  a  little  like  a  solid  and  a  little  like  a  liquid  at  the  same  time. 
Warm  it,  and  it  becomes  like  a  liquid.  Tar  that  is  very  hot  acts  like  a 
liquid  ;  as  it  cools  it  is  viscous  ;  when  it  is  perfectly  cold  it  becomes  a  solid. 
Water  is  not  viscous  ;  it  flows  freely. 

All  Bodies  are  Heavy.  —  All  bodies  —  solids,  liquids,  and  gases  —  have 
weight.  A  cubic  inch  of  any  solid  is  usually  (not  always)  heavier  than  a 
cubic  inch  of  any  liquid.  Iron  will  sink  in  water,  but  wood  will  float  on  it. 
Iron  itself  will  float  on  quicksilver.  The  gases  have  weight.  Air  has 
weight,  for  instance,  as  the  barometer  proves.  (See  page  84.) 


146 


THE  SCIENCES 


Hardness.  —  By  a  little  trouble  any  child  can  get  pieces  of  soapstone 
(talc)  (i),  rock  salt  (2),  fluor  spar  (4),  feldspar  (6),  quartz  (7).  The  numbers 
1,2,4,6,7  denote  the  degree  of  hardness  of  these  stones.  The  very  hardest 
stone  is  the  diamond,  whose  hardness  is  10.  Rock  salt  (2)  will  scratch 
soapstone  (i)  ;  feldspar  (6)  will  scratch  fluor  spar  (4)  ;  quartz  (7)  will 
scratch  all  of  them  and  will  scratch  glass,  too.  You  can  write  your  name 
on  glass  with  a  piece  of  pure  quartz.  A  diamond  will  scratch  every  stone. 
If  you  want  to  say  how  hard  a  stone  is,  you  can  give  its  hardness  in  a 
number.  Topaz  is  8  ;  it  will  scratch  quartz  but  not  diamond. 

Ductility.  — You  can  draw  some  metals  out  into  long  fine  wires.  These 
are  the  ductile  metals,  lik'e  gold,  silver,  iron,  copper,  etc.  Glass  can  be 
drawn  out  into  fine  threads  by  heating  it.  Gold  can  be  hammered  out  into 
leaves  so  thin  that  30,000  of  them,  piled  one  above  another,  would  be  only 
an  inch  high.  If  you  were  to  press  these  leaves  under  a  strong  press, 
they  would  go  back  into  a  gold  plate  by  cohesion.  (See  page  145.)  A  body 
is  called  malleable  when  it  can  be  hammered  out  into  thin  sheets.  Copper, 
for  instance,  is  very  malleable. 

Crystals.  —  Buy  three  ounces  of  alum  at  the  druggist's  and  pound  it 
into  a  fine  powder  and  put  the  powder  into  a  tumbler  full  of  very  hot  water, 
stirring  the  alum  in  with  a  glass  rod  until  all  is  dissolved.  Then  lay  a  bit 


FIG.  139.    How  TO  MAKE  ALUM  CRYSTALS 

of  stick  across  the  mouth  of  the  tumbler  with  a  short  string  hanging  down 
into  the  water.  (See  Fig.  139.)  Put  the  tumbler  in  a  cool  place  and 
look  at  it  the  next  day  and  see  the  beautiful  crystals  of  alum  that  have 
formed.  The  hot  water  kept  all  the  alum  dissolved.  As  the  water  cooled, 


PHYSICS  — APPENDIX 


H7 


some  alum  was  freed,  and  it  formed  into  its  own  kind  of  crystal.  Every- 
thing has  its  particular  way  of  crystallizing.  Alum  makes  one  kind  of 
crystal,  quartz  another. 

You  can  buy  some  rock  salt,  some  bichromate  of  potash,  and  some  blue 
vitriol  at  the  druggist's  also,  and  make  crystals  out  of  these  substances, 


FIG.  140.    DIFFERENT  FORMS  OF  SNOW  CRYSTALS 

just  as  you  made  the  alum  crystals.  Each  substance  will  crystallize  in  its 
own  way.  You  can  save  some  of  the  best  crystals  in  wide-mouthed  glass 
bottles,  tightly  corked,  and  begin  to  collect  a  cabinet  of  crystals  for  yourself. 
Freshly  fallen  snow  (that  is,  frozen  water)  makes  crystals,  as  you  can  see 
on  a  window  pane  in  the  winter  time. 


DIFFERENT  FORMS  OF  CRYSTALS 
•     148 


BOOK  III 

CHEMISTRY 

CHEMISTRY  is  the  science  that  teaches  how  to  combine  two  sub- 
stances so  as  to  produce  a  third  substance  different  from  either. 

NOTE. —  Many  chemical  experiments  can  be  tried  in  the  schoolroom  ;  but 
a  great  number  are  not  safe  to  try  there,  and  many  others  require  complicated 
or  expensive  apparatus.  Very  many,  again,  are  difficult  to  explain  to  children 
who  have  had  no  formal  teaching  in  chemistry.  For  these  reasons  the  follow- 
ing pages  are  devoted  chiefly  to  simple  and  fundamental  matters,  omitting 
details,  which  are  instructive  only  when  they  are  thoroughly  understood. 

The  children  bought  at  the  druggist's  small  bottles  of  the 
chemicals  in  the  list  below.  Every  bottle  was  labeled  with 
the  right  name,  and  they  were  warned  not  to  get  strong  acids 
on  their  hands  or  on  their  clothes. 

A  glass-stoppered  bottle  of  sulphuric  acid 

"           »  "        nitric          " 

"           "  "        hydrochloric  acid 

"           «  "        acetic  acid  (vinegar) 

A  cork-stoppered  bottle  with  sulphur 

"           "  "         iron  filings  (or  tacks) 

"           "  "         copper    "     (or  tacks) 

«          K  «         zinc        ic 

"  »  "  quicklime 

"  "  "  chalk  crayons 

«  "  "  pieces  of  pure  lead 

"  «  "  gunpowder 

"  "  "  oxyd  of  manganese 

«  «  "  sulphur  matches 
149 


150  THE  SCIENCES 

Physical  Changes  ;  Solutions.  —  "  Let  us  take  a  pinch  of  this 
common  table  salt,"  said  Jack,  "and  put  it  in  a  tumbler  of  water. 
What  happens?" 

Agnes.  The  water  will  dissolve  the  salt.  You  cannot  see  it 
any  more.  It  disappears. 

Tom.  It  is  there,  though,  in  the  tumbler;  for  the  water 
tastes  salty  when  I  wet  my  finger  with  it. 

Jack.  We  can  get  all  the  salt  back  again  if  we  want  to,  by 
pouring  the  salted  water  on  a  flat  dish  and  setting  the  dish  on 
a  hot  stove.  The  water  will  gradually  go  away,  but  our  salt 
will  be  left  on  the  plate.  The  salt  that  you  put  in  has  not 
been  changed.  It  is  the  same  salt.  It  is  fit  to  use  on  the  table, 
and  there  is  as  much  of  it  as  there  was  at  first.  Now  let  us 
try  another  experiment. 

Mixtures. — "Here  is  some  pure  sulphur,  and  here  are  some 
iron  filings.  Take  a  mortar  and  bruise  the  sulphur  in  it  till  it 
is  all  in  fine  powder.  Now  mix  the  sulphur  and  the  iron  and 
lay  the  mixture  on  this  pane  of  glass.  Can  you  boys  tell  me 
of  any  way  to  separate  the  iron  and  the  sulphur  again,  so  that 
you  can  make  one  little  pile  all  sulphur  and  another  all  iron  ?" 

Fred.  Why,  I  can  take  a  magnet  and  pull  all  the  iron  filings 
out  with  it  and  leave  the  sulphur. 

Tom.  That  is  one  way ;  but  it  is  easier  to  blow  on  the  pile, 
and  the  light  grains  of  sulphur  will  fly  off  and  leave  the  heavier 
iron. 

Jack.  That  is  a  good  way  to  separate  the  two  things  ;  but 
Fred's  way  is  the  better  if  you  want  to  save  the  sulphur. 
Well,  the  point  is  that  when  you  mixed  salt  and  water  you 
could  get  both  of  them  back  again  —  neither  was  altered  ;  and 
when  you  mixed  sulphur  and  iron  you  could  get  both  back 
again  —  neither  was  altered. 


CHEMISTRY  1 5  I 

• 

I  want  to  try  a  different  kind  of  an  experiment.  I  want  to 
mix  two  things  together  and  to  make  a  third  thing  different 
from  either  one  of  them. 

Tom.  Like  mixing  a  coat  and  a  hat  and  getting  a  pair  of 
boots  ? 

Agnes.    Oh,  Tom,  that  is  silly  ! 

Jack.  Well,  it  is  rather  funny ;  and  it  is  not  quite  so  silly 
as  you  think,  Agnes,  though  of  course  it  is  absurd  and  impos- 
sible the  way  Tom  has  said  it.  No ;  I  want  to  mix  sulphuric 
acid  and  iron,  one  a  colorless  liquid  and  the  other  a  blackish 
solid,  and  get  some  green  crystals  of  a  substance  entirely 
different  from  either  of  them. 

Chemical  Combinations.  —  Here  Jack  took  some  sulphuric  acid 
in  a  jar  and  dropped  a  few  iron  carpet  tacks  in  it.  In  a  little 
while  the  tacks  disappeared ;  they  combined  with  the  acid,  as 
people  say,  and  nothing  but  a  colorless  liquid  was  in  the  tum- 
bler as  before.  This  he  poured  into  a  flat  china  dish  which  he 
put  on  the  hot  stove.  In  a  little  while  all  the  liquid  had  dis- 
appeared and  there  were  left  beautiful  green  crystals ;  sulphate 
of  iron,  or  green  vitriol,  is  the  name  of  them.1  Then  he 
tried  exactly  the  same  experiment,  using  sulphuric  acid  and 
copper  carpet  tacks,  and  on  the  plate  there  were  left  beautiful 
blue  crystals  ;  sulphate  of  copper,  or  blue  vitriol,  is  the  name  of 
them. 

A  little  finely  powdered  quicklime  combined  with  sulphuric 
acid  produces  sulphate  of  calcium,  or  sulphate  of  lime  (calcium 
is  another  name  for  lime). 

1  To  make  green  vitriol  take  one  part,  by  weight,  of  iron  wire,  or  tacks,  with  two 
parts  of  strong  sulphuric  acid  in  four  parts  of  water  and  mix.  If  the  mixture  is 
heated,  the  combination  will  be  more  rapid.  Filter  the  resulting  fluid,  evaporate 
it  over  a  fire,  and  obtain  the  crystals. 


152  THE  SCIENCES 

"  Here,"  said  Jack,  "we  have  combined  two  things  and  in 
each  case  made  a  third  thing,  quite  unlike  either  of  them." 

Sulphuric  acid  +  iron       =  sulphate  of  iron 
"  "     +  copper  =  "          copper 

"       .    "     +  lime      =  "  lime l 

Chemistry  is  the  name  of  the  science  that  is  busy  about 
such  combinations  and  the  changes  of  one  substance  into 
another. 

"We  have  just  made  sulphate  of  lime,"  said  Jack,  "by  com- 
bining sulphuric  acid  and  quicklime.  Here  is  another  way  to 
get  it.  This  piece  of  chalk  is  made  out  of  another  acid 
(a  gas)  combined  with  lime. 

Carbonic  acid  gas  +  lime  =  carbonate  of  lime  (chalk) 

Chemical  Affinity.  —  "  It  is  as  if  the  carbonic  acid  were  a 
soldier  and  the  lime  a  prisoner.  Sulphuric  acid  is  a  stronger 
soldier  than  the  other.  If  I  pour  diluted  sulphuric  acid  on  a 
piece  of  chalk,  the  carbonic  acid  will  fly  off  in  gas  and  the  sul- 
phuric acid  will  take  the  lime  prisoner  in  its  turn,  and  we 
shall  have 

Chalk  +  sulphuric  acid  =  sulphate  of  lime. 

"  The  carbonic  acid  has  been  driven  off; 

1  To  make  blue  vitriol  take  one  part,  by  weight,  of  copper  wire,  or  tacks,  with 
ten  parts  of  strong  sulphuric  acid  (and  no  water).  Mix  and  boil  the  acid  until 
gas  rapidly  escapes.  Let  it  cool  and  carefully  pour  off  the  liquid.  Add  water  to 
what  is  left  and  evaporate  it  over  a  fire  and  obtain  the  crystals. 

To  make  sulphate  of  lime  take  one  part,  by  weight,  of  finely  pulverized  quick- 
lime with  two  parts  of  strong  sulphuric  acid  and  four  parts  of  water.  No  heat  is 
necessary.  When  the  action  ceases  evaporate  the  liquid  over  a  fire  and  obtain  the 
crystals.  The  teacher  can  repeat  these  experiments  in  the  schoolroom  after  he 
has  himself  performed  them.  Children  should  not  undertake  them. 


CHEMISTRY  153 

"  Vinegar  is  an  acid,  too.  It  is  called  acetic  acid.  Take  some 
vinegar  in  the  bottom  of  a  tumbler  and  throw  a  little  lump  of 
chalk  into  it.  What  happens  ?  You  see  the  carbonic  acid  gas 
flying  off  in  bubbles.  It  leaves  the  lime,  and  the  acetic  acid 
takes  the  lime  prisoner. 

Carbonic  acid  +  lime  =  carbonate  of  lime  (chalk) 
Chalk  +  acetic  acid  =  acetate  of  lime 

"The  carbonic  acid  has  been  driven  off  again. 

"  Chemists  say  that  sulphuric  acid  has  a  stronger  affinity  for 
(liking  for,  fondness  for)  lime  than  carbonic  acid.  It  is  just  as 
if  the  prisoner  lime  liked  to  be  a  prisoner  of  one  acid  better 
than  to  be  a  prisoner  of  the  other.  Lead,  for  instance,  likes 
to  combine  with  nitric  acid  better  than  to  combine  with 
sulphuric  acid,  and  so  with  other  substances. 

"  Chemists  study  these  likes  and  dislikes  of  the  metals, 
and  make  use  of  them.  It  is  much  easier  and  cheaper  to  get 
sulphate  of  lime  from  carbonate  of  lime  (chalk)  by  letting 
sulphuric  acid  capture  the  lime  than  it  is  to  take  simple  lime 
and  combine  it  directly  with  sulphuric  acid." 

Tom.  What  is  the  use  of  chemistry,  Jack  ?  Is  it  to  make 
new  substances  cheaply  ? 

Jack.  Partly  that.  The  scientific  use  of  it  is  to  explain  why 
two  things  combine  to  make  a  third,  and  what  is  the  best  way 
to  make  them  do  it  (for  there  are  many  different  ways).  Its 
practical  use  is  to  teach  us  how  to  make  such  things  as  gun- 
powder, glass,  soap,  vinegar,  cheese,  leather,  gas  to  burn  in  our 
houses,  bread  to  eat,  and  so  forth. 

Gunpowder,  for  instance,  is  a  mixture  of  charcoal,  sulphur,  and 
niter.1  It  is  a  mixture,  not  a  combination,  until  it  is  fired  off. 

1  Niter  is  a  combination  of  potassium  and  nitric  acid. 


154  THE   SCIENCES 

Then  it  suddenly  becomes  a  combination  of  all  three  substances, 
and  a  great  deal  of  gas  is  formed.  The  gas  expands  in  the  bar- 
rel of  the  gun,  and  in  expanding  drives  the  bullet  out.  Chemists 
have  taught  us  how  to  make  it  in  the  best  way.  During  our  Revo- 
lutionary War  the  powder  was  so  poor  that  men  were  seldom  killed 
outright  as  far  off  as  a  hundred  yards.  Nowadays  powder  will 
drive  a  bullet  with  force  enough  to  kill  at  2000  yards  or  more. 

Tom.  I  have  seen  a  book  about  Benjamin  Franklin  that  says 
he  advised  the  Congress  not  to  arm  the  soldiers  in  the  Revolu- 
tionary War  with  guns,  but  with  bows  and  arrows,  because  they 
could  kill  nearly  as  far  off  with  arrows  as  with  muskets  and 
because  they  could  shoot  much  faster. 

Jack.  It  sounds  absurd  nowadays,  but  it  was  not  at  all  absurd 
then.  The  muskets  were  better  than  bows  and  arrows,  even 
then,  but  not  so  very  much  better.  The  powder  was  especially 
poor.  Chemists  would  laugh  at  it  nowadays. 

Mary.  What  do  chemists  know  about  bread,  Jack  ?  I  think 
the  cook  knows  more  than  they  do. 

Jack.  I  have  no  doubt  the  cook  can  make  bread  better  if  you 
give  her  the  right  kinds  of  flour  and  yeast,  and  so  forth  ;  but 
the  chemist  tells  how  to  make  the  right  kinds.  She  uses  what 
he  has  invented.  There  are  dozens  of  different  kinds  of  bread 
for  soldiers  and  sailors  and  invalids.  They  were  invented  by 
chemists  so  as  to  be  healthful,  or  to  keep  without  spoiling  on 
long  voyages.  The  cook  could  not  do  that.  All  the  beautiful 
dyes  for  silk  and  wool  and  cotton  (different  dyes  for  each  kind  of 
stuff),  all  the  paints,  all  the  inks  used  for  writing  and  printing, 
and  a  thousand  things  of  the  sort  were  invented  by  chemists. 
Why,  chemists  nowadays  make  indigo — by  mixing  carbon  hydro- 
gen, nitrogen,  and  oxygen  in  the  right  proportions — that  is  just 
as  good  as  the  indigo  that  grows  on  the  plant. 


CHEMISTRY  155 

Composition  of  the  Air.  —  The  air  of  the  atmosphere  is  prin- 
cipally made  up  of  a  mixture  of  two  invisible  gases  called  oxygen 
and  nitrogen.  Both  are  invisible  and  so  is  the  air^  the  mixture 
of  the  two.  Water  is  a  combination  of  oxygen  and  hydrogen. 
Oxygen  gas  can  be  prepared  by  heating  a  mineral  called  oxyd 
of  manganese.  It  is  made  out  of  manganese  combined  with 
oxygen.  When  the  mineral  is  heated  the  oxygen  goes  off  as  a 
gas  and  can  be  collected  in  a  jar  under  water.  (See  Fig.  141.) 


FIG.  141.     PREPARATION  OF  OXYGEN  GAS 

Heat  powdered  oxyd  of  manganese  in  a  test  tube  one-third  full.  The  oxygen  gas  will  be 
driven  off  by  the  heat  and  can  be  collected  over  water  in  a  jar  turned  upside  down. 
Afterwards  slide  a  sheet  of  glass  under  the  jar  so  as  to  close  it  and  turn  the  jar  right 
side  up  till  the  gas  is  wanted  for  other  experiments. 

Nitrogen  gas  can  be  prepared  by  burning  a  bit  of  phosphorus 
(not  bigger  than  a  green  pea)  under  a  glass  containing  air  (air 
is  oxygen  and  nitrogen  mixed).  The  phosphorus  burns  up  all 
the  oxygen  in  the  air  and  leaves  only  nitrogen. 

In  100  pounds  of  air,  23  pounds  are  oxygen,  and  77  pounds 
are  nitrogen.  This  is  the  air  we  breathe.  If  a  live  animal  (a 
mouse,  for  instance)  is  put  into  a  glass  jar  that  contains  nitro- 
gen and  no  oxygen,  it  dies.  It  is  not  the  nitrogen  that  kills  it, 
but  the  lack  of  oxygen.  To  have  life  we  must  breathe ;  to 


156  THE  SCIENCES 

breathe  there  must  be  enough  oxygen.  Nitrogen  helps  plants 
to  live,  but  for  men  and  animals  there  must  be  plenty  of  oxygen. 

Combustion.  —  Combustion  is  burning.  When  a  match  burns 
there  is  combustion.  All  combustion  is  the  combination  of 
something  with  oxygen.  When  a  match  burns,  the  sulphur 
on  its  head  unites  with  the  oxygen  of  the  air  about  it.  When 
a  coal  fire  burns,  the  coal  unites  with  the  oxygen  of  the  air. 
Combustion  is  rapid  in  the  case  of  the  match  or  of  the  coal,  but 
it  is  not  always  so  quick.  Sometimes  it  is  slow.  When  iron 
rusts,  as  we  say,  the  iron  of  the  outside  layers  combines  with 
the  oxygen  of  the  air  and  makes  iron  rust.1  Rusting  is  a  sort  of 
slow  fire  without  flame,  and  the  iron  rust  that  is  left  is  the 
ashes.  By  taking  great  pains  we  could  even  measure  the  heat 
that  is  thrown  off  while  the  iron  is  rusting.  A  similar  kind  of 
slow  fire,  without  flame,  takes  place  in  our  own  body.  Air  is 
breathed  into  our  lungs  and  meets  the  blood  there.  The  oxy- 
gen of  the  air  is  carried  to  all  parts  of  the  body  by  the  blood, 
and  our  fat  and  food  are  actually  burned  (slowly  and  without 
flame  of  course)  in  the  body.  That  is  the  way  the  temperature 
of  the  body  is  kept  up  to  98°  when  the  air  outside  may  be 
down  to  zero.2 

A  very  pretty  experiment  can  be  tried  by  lighting  a  match, 
blowing  it  out,  and  then  putting  the  glowing  red  end  into  a  jar 
of  oxygen.  The  match  instantly  bursts  into  flame  and  burns 
very  brightly.  Blow  out  the  match  and  try  the  experiment 
again.  The  match  will  burst  into  flame  by  itself,  as  it  were, 
so  long  as  there  is  any  oxygen  left  in  the  jar.  Even  the 
diamond  will  burn  in  oxygen,  though  it  cannot  be  burned  in  air. 

1  Silver  and  gold  do  not  rust,  and  that  is  why  they  are  used  for  watch  cases, 
coins,  and  tableware  —  spoons  and  forks. 

2  The  average  temperature  of  the  healthy  human  body  is  between  98°  and  99°. 


OF  THE 

UNIVERSITY 

OF 


CHEMISTRY 


157 


Hydrogen  gas  can  be  prepared  by  putting  some  water  and 
a  few  scraps  of  zinc  in  a  stoppered  bottle  (see  Fig.  142)  and  by 
adding  hydrochloric  acid,  which  is  a  combination  of  hydrogen 
and  chlorine. 


Zinc  +  water  I  -f 


hydrogen  +  chlorine  I  = 

j  water  +  chloride  of  zinc    /  +  hydrogen 

1  (these  stay  in  the  bottle)  C      (this  goes  over  in  the  tube) 

The  hydrogen  can  be  collected  as  the  oxygen  was  before. 

Water. —  If  hydrogen  gas  is  burned  in  oxygen  (the  experi- 
ment is  not  a  safe  one  for  the  schoolroom),  water  is  pro- 
duced. Or,  again,  pure  water  can  be  separated  by  electricity 


FIG.  142.     PREPARATION  OF  HYDROGEN  GAS 

Put  water  and  scraps  of  zinc  into  the  stoppered  bottle  and  add  hydrochloric  acid  through 
the  straight  funnel.  The  freed  hydrogen  gas  will  escape  through  the  bent  tube  and  can 
be  collected  under  water  and  kept  for  use  in  a  jar.  (Leave  the  jar  upside  down.)  l 

Hydrogen  is  one  of  the  lightest  of  gases,  and  it  is  exactly  suitable  for  the  filling  of  balloons. 
Fourteen  cubic  feet  of  hydrogen  weighs  only  as  much  as  one  cubic  foot  of  air.  This 
gas  is  expensive,  however,  and  most  balloons  are  filled  with  ordinary  illuminating  gas, 
v/hich  is  much  cheaper  than  hydrogen  although  not  so  good  for  the  purpose. 

into  hydrogen  and  oxygen.  These  two  gases,  both  invisible, 
combine  into  water — a  liquid;  and  ice  —  a  solid  —  is  nothing 
but  very  cold  water.  That  is,  solid  ice  is  made  out  of  two  gases. 

1  None  of  these  experiments  are  to  be  tried  by  children. 


158  THE  SCIENCES 

Chemical  Elements.  —  When  a  chemist  sees  a  substance  new 
to  him — a  mineral,  for  instance  —  the  first  thing  he  tries  to  find 
out  is  whether  it  is  a  combination  of  substances  that  he 
knows  already.  For  example,  he  finds  that  salt  is  made  out 
of  chlorine  (a  gas)  and  sodium  (a  very  light  metal).  Then  he 
tries  to  see  if  he  can  separate  chlorine  into  any  other  two 
substances ;  he  cannot  do  it,  or,  at  any  rate,  chemists  have  not 
done  it  so  far.  Neither  have  they  separated  sodium  into  any 
simpler  things.  Substances  that  cannot  be  separated  into 
simpler  substances  are  called  elements.  Here  is  a  list  of  the 
most  familiar. 

METALS 

Aluminum  Potassium 

Calcium  Quicksilver  (a  liquid  metal) 

Copper  *  Nickel 

Gold  Silver 

Iron  Tin 

Lead  Zinc 
Sodium 

NON-METALS 

*  Arsenic  *  Iodine 

Carbon  Nitrogen  (a  gas) 

Chlorine  (a  gas)  Oxygen  (a  gas) 

Hydrogen  (a  gas)  *  Phosphorus 

Sulphur 

There  are  twenty-two  elements  named  in  this  table.  If  all 
known  elements  were  included,  there  would  be  about  seventy 
names. 

Every  single  thing  on  the  earth  that  you  can  name  is  made 
up  of  one,  or  two,  or  three,  or  more  of  these  seventy  elements; 
and  it  is  exceedingly  interesting  to  remember  that,  so  far  as 
we  know,  everything  on  the  sun,  the  moon,  and  the  planets  is 
made  up  in  the  same  way. 


CHEMISTRY  159 

Some  of  the  stars  and  some  of  the  nebulae  may  have  elements 
unknown  to  our  chemists,  but  the  solar  system — the  sun, 
the  earth,  and  the  planets  —  seem  to  be  all  of  a  piece.  Ninety- 
nine  hundredths  of  all  the  matter  in  the  solar  system  is  made 
up  of  the  eighteen  elements  whose  names  are  not  marked  with 
an  asterisk  (*)  in  the  table  just  preceding. 

Chemical  Compounds.  —  Nearly  all  the  substances  that  we 
handle  are  compounds,  not  elements. 

Diamond  is  pure  carbon. 

The  black  lead  of  a  lead  pencil  is  nearly  pure  carbon. 

Sugar  is  carbon,  hydrogen,  and  oxygen. 

Human  hair  is  carbon,  hydrogen,  oxygen,  nitrogen,  and 
sulphur. 

Indigo  is  carbon,  hydrogen,  oxygen,  and  nitrogen. 

Quinine  is  carbon,  hydrogen,  nitrogen,  oxygen,  and  sulphur. 

Air  is  a  mixture  of  oxygen  and  nitrogen. 

Water  is  oxygen  and  hydrogen. 

Steel  is  iron,  with  some  nickel,  phosphorus,  etc. 

Wood  is  chiefly  carbon,  oxygen,  hydrogen,  and  nitrogen. 

Leather  is  chiefly  carbon,  oxygen,  hydrogen,  and  nitrogen. 

Human  flesh  is  chiefly  carbon,  hydrogen,  and  oxygen,  with 
some  sulphur,  nitrogen,  phosphorus,  calcium,  sodium,  potassium, 
and  magnesium. 

Fat  is  carbon,  hydrogen,  and  oxygen. 

Lean  is  carbon,  hydrogen,  oxygen,  nitrogen,  and  sulphur. 

Milk  is  water  (oxygen  and  hydrogen),  containing  fat,  etc. 
(carbon,  hydrogen,  oxygen,  nitrogen,  and  sulphur). 


FIG.  143.     DIFFERENT  FORMS  OF  CLOUDS 

a,  cirrus;  b,  cumulus;  c,  stratus;  d,  nimbus  (rain  cloud). 
160 


BOOK  IV 
METEOROLOGY 

THE  SCIENCE'  OF  THE  WEATHER 

The  Atmosphere ;  the  Colors  of  Sunset.  ~  "  I  wonder  why  it 
is,"  said  Agnes,  "that  sunsets  and  sunrises  are  red.  It  is  the 
same  sun  at  noon  and  at  sunset,  and  the  same  sky ;  but  sunsets 
are  red,  and  the  sky  is  never  red  at  noon." 

Jack.  There  are  two  main  reasons,  Agnes.  In  the  first 
place,  we  are  looking  at  the  sun  through  an  air  that  is  full  of 
dust ;  and  in  the  second  place,  the  more  dust  you  look  through 
the  redder  a  thing  looks  that  is  beyond.  At  sunset  (and  sun- 
rise) you  see  the  sun  through  a  greater  thickness  of  air  than 
you  do  at  noon. 

Mary.    I  do  not  understand  how  that  is. 

Jack.    Tom,  see  if  you  can  explain  it  by  a  little  drawing. 
Tom.    Is  n't  it  like  this  ?     When  the  sun  is  nearly  overhead 
at  noon  we  see  it  through  a  less  thickness  of  air  than  when  it 
is  setting  (or  rising).     (See  Fig.  144.) 

Jack.  That  is  right.  The  greater  the  thickness  of  air  the 
more  dust  there  is  in  it ;  and,  moreover,  the  more  dust  the 
redder  the  sun  looks. 

Agnes.    How  do  you  know  that,  Jack  ? 

Jack.  Well,  you  could  try  the  experiment  by  pointing  a  long 
wooden  box  filled  with  dusty  air  at  the  sun,  and  then  by  taking 

161 


162 


THE  SCIENCES 


a  box  twice  as  long  and  doing  the  same  thing.  But  the  sim- 
plest proof  is  this:  In  1883  there  was  a  huge  volcanic  erup- 
tion of  a  mountain  in  Java,  called  Krakatoa.  The  whole  air 
for  hundreds  of  miles  round  was  darkened  with  the  dust  from 
the  volcano.  The  winds  scattered  this  dust  round  the  whole 
earth,  so  that  for  two  years  afterwards  all  the  sunsets  in 

Sun, 
at  noon. 


•Sun,  sett  ing ^ 


FIG.  144 

A  person  on  the  earth's  surface  at  A  sees  the  sun  overhead  at  noon  through  a  thickness  of 
air  (AS),  and  the  sun  at  sunset  through  a  thickness  of  air  (AC).  AC  is  considerably 
greater  than  AB. 

Europe  and  America  were  very  red  indeed,  much  redder 
than  usual.  There  was  an  extra  amount  of  dust  in  the  air 
at  that  time,  and  so  the  sunsets  and  sunrises  were  redder 
than  usual.  It  is  the  same  thing  in  sand  storms  on  deserts. 
The  sun  looks  red  through  them. 

Fred.    Suppose  you  should  go  up  on  a  high  mountain,  what 
then  ? 


METEOROLOGY  163 

Jack.  The  higher  up  you  go  the  less  dust  you  look  through. 
If  you  are  on  Mount  Washington  in  the  White  Mountains  (5000 
feet  high),  or  on  Mount  Hamilton  in  California  (4000  feet),  the 
sky  looks  very  pure  and  blue,  and  if  you  go  to  the  top  of  the 
high  Alps  or  on  Pikes  Peak  (14,000  feet),  the  sky  is  a  dark 
violet  color  —  it  begins  to  look  a  little  black  even. 

Fred.    And  in  balloons  ? 

Jack.  It  is  blacker  yet.  The  less  dust  you  are  looking  through 
the  whiter,  or  the  bluer  rather,  the  sun  looks  to  you.  If  you  were 
quite  outside  the  earth's  atmosphere — on  the  moon,  for  instance 
—  the  sun  would  not  look  yellow  at  all ;  it  would  be  bluish. 

Mary.    Where  does  the  dust  come  from,  Jack  ? 

Jack.  Oh,  from  dusty  plains,  from  smoke,  the  pollen  of  plants, 
and  from  volcanoes.  Just  think  of  the  millions  of  tons  of  coal 
that  are  burned  every  winter. 

Mary.  Well,  then,  why  doesn't  the  air  become  thick  with 
smoke  by  and  by  and  stay  so  ? 

Jack.    See  if  you  can  answer  that,  Tom. 
Tom.    Is  it  because  every  rain  storm  carries  the  dust  particles 
down  with  the  raindrops  ?     I  have  noticed  that  the  air  is  clearer 
after  rain. 

Jack.  Yes,  that  is  a  good  reason ;  and  a  great  part  of  the 
dust  falls  on  the  ocean,  too,  and  is  lost  in  that  way. 

Twilight. — "If  you  will  look  out  any  evening  half  an  hour 
after  sunset,  you  will  see  a  faint  arch  in  the  sky  in  the  west 
that  is  a  little  brighter  than  the  rest.  That  is  the  twilight 
arch,  and  it  is  caused  by  the  sun's  rays  reflected  and  scattered 
from  dust  high  up  in  our  air.  You  had  better  look  for  it  on 
the  next  clear  evening.  It  is  easy  to  see. 

Dust  in  the  Atmosphere.  —  "  One  of  the  things  that  physicians 
want  to  know  is  how  pure  the  air  is  at  any  place  —  how  free 


1 64 


THE  SCIENCES 


from  dust.  They  put  little  plates  of  glass  covered  with  sticky 
varnish  out  of  doors  and  then  count  the  pieces  of  dust  on 
the  glass  with  a  microscope.  High  mountains  and  the  snowy 
arctic  regions  have  the  purest  air  of  course  ;  but  even  there 
there  is  a  great  deal  more  than  you  would  think." 

The  Rainbow.  —  "Is  the  rainbow  caused  by  dust,  Jack?  "  said 
Agnes  ;  "part  of  it  is  red." 

Jack.  No,  Agnes  ;  that  is  different.  You  see  all  the  colors 
are  in  the  rainbow,  not  red  alone. 

The  white  light  from  the  sun  is  split  up  into  colors  by  each 
raindrop  much  as  it  would  be  by  a  glass  prism,  and  then  the 
light  is  scattered  by  the  different  drops  as  light  is  scattered 


FIG.  145.     WHITE  LIGHT  ENTERING  A  RAINDROP  is  SPLIT  UP 
INTO  COLORED  LIGHTS 

A  white  sunbeam  enters  a  hollow  raindrop,  and  its  different  colors  are  separated  by  the 
water  of  the  drop  as  they  would  be  by  a  prism  of  glass.  The  white  color  is  separated 
into  red,  yellow,  blue,  and  so  forth,  and  is  refracted  by  the  drop  down  to  the  ground 
where  you  are  standing.  (See  Fig.  146.)  You  see  the  drops  by  these  refracted  colors  — 
red,  yellow,  blue  —  and  all  of  these  colors  show  in  the  rainbow. 


METEOROLOGY 


from  mother-of-pearl  shells.     It  is  not  very  easy  to  explain  in 
simple  words,  but  that  is  the  main  cause. 

Halos.  —  "You  have  seen  rainbows  round  the  moon,  haven't 
you  ?  and  halos  —  bright  circles  —  round  the  moon  ?    They  are 


Sometimes  two  bows  are  seen.  Both  are  formed  in  much  the  same  way.  The  ordinary  bow 
is  formed  by  sunlight  that  enters  the  top  of  the  raindrops  and  is  refracted  to  the  eye. 
The  secondary  bow  is  formed  by  sunlight  that  enters  the  bottom  of  the  raindrops. 
(Examine  the  picture  carefully.)  SSS'S'  are  rays  from  the  sun ;  HH'  is  the  horizon. 
The  center  of  the  bow  is  always  exactly  opposite  to  the  sun  from  where  you  stand. 

caused  by  little  prisms  of  ice  floating  high  up  in  the  atmosphere, 
which  scatter  the  moonlight  in  a  regular  way." 

Fog  and  Clouds.  —  "The  air  is  full  of  dust  that  we  can  see," 
said  Jack,  "  and  it  is  full  of  the  vapor  of  water  that  we  cannot 


1 66 


THE  SCIENCES 


FIG.  147.     A  COMPLETE  SOLAR  HALO  (parhelion,  sundog) 

Sometimes  the  complete  halo  is  seen  as  in  the  picture,  but  more  often  only  parts  of  it. 
These  halos  are  caused  by  light  refracted  from  small  prisms  of  ice  in  our  atmosphere. 

see,  too.  When  I  put  a  pan  of  water  out  of  doors,  Agnes, 
what  becomes  of  the  water  ?  " 

Agnes.  It  disappears  somehow,  if  there  is  not  much  of  it. 
I  don't  know  where  it  goes. 

Tom.  It  evaporates ;  it  rises  up  into  the  air  like  a  gas. 
I  suppose  it  is  a  gas. 

Jack.  Yes,  it  is  a  gas,  like  invisible  steam.  Real  steam  is 
invisible,  and  water  vapor  is  invisible.  When  the  water  vapor 
in  the  air  turns  into  visible  water  what  do  you  see  ? 


METEOROLOGY  167 

Agnes.    Fogs  and  clouds  and  mist. 

Mary.    Yes,  and  rain  and  dew. 

Jack.  Mist  and  fog  are  made  of  millions  and  millions  of 
little  drops  of  water. 

Agnes.  Why  don't  they  fall  down  in  rain,  then,  Jack  ? 
Water  is  heavy. 

Jack.  The  drops  are  hollow,  and  they  are  very  small  and  they 
float  in  the  air  just  as  soap  bubbles  do. 

Dew.  — "  When  you  breathe  on  a  cold  windowpane  the 
invisible  water  vapor  in  your  breath,"  said  Jack,  "  condenses  on 
the  pane  and  makes  a  mist  which  is  just  like  the  dew  that  falls 
at  night.  Take  a  tumbler  of  ice  water  and  set  it  in  a  warm 
room  and  you  will  see  dew  form  on  the  outside  of  the  tumbler. 
The  cold  tumbler  condenses  the  invisible  water  vapor  just  as 
the  cold  water  of  a  pond  condenses  the  vapor  of  the  air  above 
it  into  a  fog  or  mist.  The  reason  is  because  a  cubic  foot  of 
warm  air  can  hold  more  water  vapor  than  a  cubic  foot  of  cold 
air.  When  you  cool  air,  no  matter  how  you  do  it,  you  squeeze 
some  of  its  water  vapor  out  of  it." 

Tom.  When  the  sun  rises  the  fogs  over  ponds  vanish.  Is 
that  because  all  the  air  gets  warmer  and  can  hold  more 
vapor  ? 

Jack.  Exactly  so,  and  when  all  the  air  is  warm  you  have  no 
clouds  either.  Clouds  are  a  sure  sign  that  the  air  where  they 
are  is  colder  than  the  other  air  in  the  neighborhood. 

Agnes.    How  high  are  the  clouds,  Jack  ? 

Jack.  Oh,  they  are  at  very  different  heights.  Why,  don't 
you  know,  Agnes,  that  you  are  sometimes  in  the  very  midst  of 
a  rain  cloud?  The  cirrus  clouds  (see  Fig.  143)  are  sometimes 
ten  miles  high,  but  usually  less.  They  are  probably  made  of 
little  ice  crystals,  for  the  air  at  that  height  is  very  cold  indeed. 


1 68  THE   SCIENCES 

The  cumulus  clouds  are  a  mile  high,  or  so.  The  stratus 
clouds  are  the  lowest. 

Tom.  If  clouds  are  made  of  hollow  water  drops  like  soap 
bubbles  floating  in  the  air,  how  is  it  that  we  ever  have  rain  ? 
Why  don't  the  bubbles  always  float? 

Jack.  You  have  seen  two  soap  bubbles  come  together  and 
burst?  They  become  nothing  but  two  heavy  drops  of  water,  or 
even  one  drop,  and  the  water  falls.  That  is  rain. 

Rain.  —  "  A  little  sphere  of  water  that  is  not  hollow  is  a  good 
deal  heavier  than  the  air,  and  a  hollow  sphere  of  water  is  often 
lighter  than  air.  There  are  millions  of  drops  in  a  cloud,  and 
when  they  are  blown  about  by  winds  they  come  into  collision 
and  fall  in  rain. 

Size  of  Raindrops.  —  "The  next  time  it  rains  try  to  measure 
the  diameter  of  the  raindrops.  It  is  not  very  easy,  but  you 
can  find  some  way  to  do  it.  I  leave  it  to  you  boys  to  invent  a 
way.  The  raindrops  of  a  heavy  pattering  summer  shower  are 
large  —  about  a  tenth  of  an  inch  in  diameter.  Fine  rain  is 
made  of  drops  one  twentieth  to  one  fiftieth  of  an  inch  in  size." 

Hail  and  Snow  and  Sleet.  —  "I  suppose  hail  is  nothing  but 
frozen  rain,"  said  Mary. 

Agnes.    And  snow  and  sleet,  too,  for  that  matter. 

Tom.  Sleet  is  nothing  but  snow  that  is  driven  about  by  the 
wind.  In  calm  weather  you  get  the  little  snow  crystals ;  but 
when  the  wind  blows,  a  dozen  of  them  are  blown  into  one  and 
they  come  down  in  little  lumps  of  ice ;  sleet,  that  is. 

Jack.  Or  else  the  snow  falls  through  a  layer  of  rather  warmer 
air  and  is  partly  melted. 

The  Snow  Line.  —  "The  higher  up  you  go,"  said  Jack,  "the 
colder  is  the  air,  and  by  and  by  you  come  to  a  height  above 
which  there  is  never  rain,  only  snow.  That  is  the  line  of 


METEOROLOGY 


169 


perpetual  snow.  In  our  Rocky  Mountains  the  snow  line  is  about 
1 3,000  feet  or  so.  Above  that  height  the  snow  never  melts  at 
all,  and  you  have  snow  mountains.  In  Alaska  the  snow  line  is 
nearly  at  the  level  of  the  sea.  That  is  one  reason  why  Alaska 
scenery  is  so  impressive.  A  low  snow  line  makes  fine  mountains. 
Uses  of  Snow.  —  "  If  no  snow  fell  in  the  winter  time,  seeds 
would  have  a  hard  time  to  grow,  as  the  ground  would  be  frozen 


FIG.  148.     SNOW  CRYSTALS 
Notice  that  all  snow  crystals  are  six  sided. 

stiff  ;  but  the  snow  fall  covers  it  up  like  a  blanket.  The  ground 
is  not  frozen  so  very  deep,  and  the  seeds  have  a  chance. 

Irrigation.  —  "  Snow  has  another  great  use.  When  it  melts 
in  the  spring  the  water  can  be  used  for  irrigating  arid  lands. 
We  in  the  United  States  let  our  snow  go  mostly  to  waste. 
We  ought  to  save  it  in  great  reservoirs  in  the  western  and 
southwestern  states  and  let  it  out  during  the  summer  when  it 
is  sadly  needed.  Nevada  and  Arizona  and  other  states  could 
be  made  into  gardens  if  people  would  take  a  little  trouble." 

Tom.  That  is  something  for  the  government  to  do.  The 
government  must  build  the  reservoirs,  and  the  people  will  do 
the  rest. 


THE  SCIENCES 


Frost.  —  "  I  suppose  frost  is  nothing  but  frozen  dew,"  said 
Mary. 

Jack.    It  is  not  quite  that,  Mary,  though  it  looks  so.     The 
dew  does  not  fall  first  as  water  and  then  freeze ;  but  it  really  is 

water  vapor  frozen  in  the  air,  and 
it  falls  in  fine  spikelets  of  ice  and 
covers  everything. 

Rainfall.  —  "  How  much  rain 
falls  in  a  year,  Jack?"  said  Fred. 

Jack.  Fred,  that  is  like  asking 
how  long  the  nose  of  a  man  is. 
Why,  in  some  parts  of  the  world 
almost  no  rain  falls  —  on  the 
deserts  of  Sahara  and  of  Arizona, 
for  instance.  The  average  rainfall 
of  the  whole  world  is  about  thirty- 
three  inches  in  each  year ;  the 
water  would  be  about  a  yard  deep 
at  the  end  of  a  year  if  all  of  it 

The  arrow  points  to  the  direction  from      were  Saved if  it  did  not  get  into 

the  soil.     But  there  is  an  enormous 
difference   in  rainfall  at   different 
places.     On    the    arid    plains    of 
Arizona  there  are  often  less  than 
two  inches  a  year.     In  some  parts 
of  the  Himalaya  Mountains  forty 
once  for  all,  so  as  to  point  north,    feet  of  rain  fall  in  a  year, 
east,  south,  west.  Rainfall  and  Crops.  —  "  Wheat 

will  not  grow  by  itself  where  the  rainfall  is  less  than  about 
eighteen  inches  a  year,  unless  there  are  plenty  of  fogs.  In  the 
arid  (dry)  regions  the  farmers  have  to  irrigate  their  crops." 


FIG.  149.     ONE  FORM  OF 
WIND  VANE 


which  the  wind  is  coming.  If  you 
should  move  the  arrow  so  as  to  point 
in  any  other  direction  and  then  let 
go  of  it,  you  can  see  that  the  pressure 
of  the  wind  on  the  tail  of  the  vane 
would  soon  bring  it  back.  A  wind 
vane  put  into  a  rapid  stream  of  water 


METEOROLOGY 


171 


Winds.  —  "A  wind,"  said  Jack,  "is  a  current  of  air  moving 

near  the  surface  of  the  earth.     How  can  you  tell  which  way 

the.  wind  blows  ?  " 

Mary.    A  wind  vane  will  do  that.     (See  Fig.  149.) 

Force  of  the  Wind.  —  "Here  is  a  table,"  said  Jack,  "that 

scientific  men  and  sailors  use  to  express  the  velocity  of  the 

wind,  or  else  its  pressure  on  a  square  foot. 


SCALE 

DESCRIPTION 

VELOCITY   IN 
MILES  PER  HOUR 

PRESSURE  IN  POUNDS 
PER  SQUARE  FOOT 

O 

Calm 

0 

O 

I 

Very  light  breeze 

2 

3 

T017 

2 

Gentle  breeze 

7    or  less 

T2ijV  or  less 

3 

Fresh  breeze 

ii 

T6o4o 

4 

Strong  wind 

1  8  or  more 

IT^  or  more 

5 

High  wind 

27 

3i6oV 

6 

Gale 

36 

6i& 

7 

Strong  gale 

45 

10 

8 

Violent  gale 

58 

17 

9 

Hurricane 

76 

29 

10 

Most  violent  hurricane 

95 

45 

"  You  can  describe  a  wind  by  using  this  little  table.  A  wind 
that  blows  about  eighteen  miles  an  hour  —  one  that  would  carry 
a  feather  or  a  little  toy  balloon  about  eighteen  miles  in  sixty 
minutes — is  called/<?z/r  (4).  (See  the  first  column  of  the  table.) 
Such  a  wind  presses  on  every  square  foot  of  a -house  nearly  two 
pounds.  Hurricanes  travel  at  the  rate  of  seventy-six  miles  an 
hour — faster  than  express  trains — and  press  on  every  square 
foot  of  houses  nearly  thirty  pounds." 

Agnes.    And  the  houses  are  often  blown  down,  too. 


172  THE  SCIENCES 

Jack.  They  are  n't  built  to  resist  such  winds.  We  very  seldom 
have  them  in  our  part  of  the  world,  I  'm  thankful  to  say. 

Causes  of  the  Winds.  —  "  Whenever  the  surface  of  the  earth 
is  warm,"  said  Jack,  "the  air  over  that  part  rises  and  other  air 

N.POLE 


FIG.  150.     A  MAP  OF  THE  GENERAL  WINDS  OF  THE  EARTH 

The  arrows  show  their  general  direction.  The  dark  spots  mark  places  where  there  is 
much  rain.  These  winds  blow  over  large  regions  of  the  earth.  There  are  particular 
winds  over  smaller  regions ;  but  these  are,  of  course,  not  shown  on  the  map. 

from  a  coWer  place  flows  in  to  take  its  place.  If  you  boys 
build  a  bonfire,  the  air  rises  and  the  smoke  rises  with  it. 
Other  air  comes  in  to  take  its  place,  and  if  your  fire  was  big 
enough  —  if  a  city  were  burning  —  it  would  create  a  really 


FIG.  151.     DIAGRAM  TO  SHOW  HOW  WINDS  ARISE 

If  any  region  (D)  is  warmer  than  near-by  regions  (C,C),  the  air  over  D  is  warmed  and  rises. 
As  it  rises  it  cools,  and  the  air  near  B,B  moves  downwards  and  inwards  to  take  its  place. 
The  air  over  a  bonfire  moves  in  this  way,  and  we  have  a  little  local  wind.  The  air  over 
a  large  part  of  the  Mississippi  valley  may  move  in  the  same  way  for  like  reasons,  and 
then  we  have  winds  covering  several  states. 


I.   In  January 


II.    In  July 


FIG  152.    WINDS  OF  THE  ATLANTIC  OCEAN 

The  arrows  show  which  way  the  winds  blow.     Charts  like  these  are  made  for  every  ocean 
and  for  each  month,  and  sailing  ships  go  by  tracks  where  the  winds  are  favorable. 

173 


174  THE  SCIENCES 

strong  wind.  The  sun  warms  the  hot  regions  of  the  earth, 
near  the  equator,  more  than  the  arctic  regions  ;  the  hot  air  rises 
and  the  cold  arctic  air  flows  southwards  to  take  its  place." 

Tom.  You  have  to  add  that  the  earth  is  turning  round  all 
the  time  and  so  the  winds  do  not  flow  straight  to  the  equator 
but  in  spirals. 

Jack.  The  sun  is  warming  the  earth  all  day  —  land  and 
water,  mountains  and  valleys ;  and  all  night  the  heat  from  the 
warmed  places  is  rising  up. 

Land  and  Sea  Breezes.  —  "  The  land  gets  warm  more  quickly 
than  the  sea,  so  that  all  day  the  breeze  blows  from  sea  to  land. 


FIG.  153.     THE  SUN  (S)  SHINING  ON  THE  EARTH  ILLUMINATING  AND 

HEATING   THE    HEMISPHERE   TURNED   TOWARDS    HIM 

It  is  daytime  in  that  hemisphere.     As  the  earth  revolves  on  its  axis  (NS)  every  twenty-four 
hours  both  hemispheres  are  lighted  and  heated  in  turn. 

At  night  the  land  gets  cool  sooner  than  the  sea,  so  that  all 
night  the  breeze  blows  from  land  to  sea.  The  next  time  you 
go  to  the  seashore  see  if  this  is  not  true.  Of  course  there  will 
be  other  winds,  too ;  but  every  hot  day  you  will  notice  the  sea 
breeze  that  springs  up  in  the  morning  and  blows  till  nightfall." 
Weather.  —  "  Weather  depends  upon  a  great  many  things," 
said  Jack.  "  See  if  you  children  can  tell  me  some  of  them." 


METEOROLOGY  1 75 

Agnes.  Well,  we  have  warm  days  and  cooler  nights  because 
the  earth  turns  round.  We  are  in  the  sun's  rays  in  the  day- 
time and  out  of  them  at  night.  (See  Fig.  153.) 

Mary.  And  we  have  cold  winters  and  warm  summers  because 
—  I  don't  believe  I  quite  know  why.  Is  it  because  the  earth 
is  nearer  to  the  sun  in  summer  ? 

Jack.  No,  the  earth  is  a  little  nearer  to  the  sun  in  Decem- 
ber and  January  than  it  is  in  June  and  July  —  a  little,  though 


FIG.  154.    THE  EARTH  IN  ITS  PATH  ROUND  THE  SUN 

The  earth  is  at  A  in  December,  at  B  in  March,  at  C  in  June,  at  D  in  September.  NS  is 
the  earth's  axis,  and  N  is  the  earth's  north  pole  (in  all  four  positions).  At  A  (December) 
the  arctic  regions  are  dark.  As  the  earth  turns  round  on  its  axis  a  person  at  N  is  not 
brought  into  the  light.  In  the  northern  hemisphere  in  March  the  days  are  shorter 
than  the  nights.  As  the  earth  turns  a  person  anywhere  in  the  northern  hemisphere 
is  in  the  lighted  half  of  the  earth  for  a  shorter  time  than  in  the  dark.  But  in  June 
(C)  a  person  in  the  northern  hemisphere  is  longer  in  the  light  than  in  the  dark  —  longer 
in  the  region  heated  by  the  sun. 

not  much ;  there  is  a  different  reason,  Mary.    (See  Fig.  1 54.) 

Storms.  —  "  Our  weather  depends  on  the  earth's  turning  on 

its  axis  then,"  said  Jack,  "  and  on  its  motion  round  the  sun. 

Those  causes  are  working  all  the  time.    Then  there  are  storms  that 


1 76 


THE  SCIENCES 


travel  over  the  whole  country  from  west  to  east l  and  others  that 
come  up  from  the  Gulf  of  Mexico  along  the  Gulf  Stream.  These 
storms  reach  us,  and  our  weather  on  Thursday,  we  may  say,  depends 
upon  the  weather  some  one  else  had  on  Monday.  The  Weather 
Bureau  in  Washington  gets  reports  of  all  the  storms  in  the  whole 
country  by  telegraph  several  times  a  day  and  makes  up  a  pre- 
diction about  the  weather  we  are  going  to  have.  You  see  the 
Weather  Bureau  predictions  in  the  newspaper  every  day.2 

Storm  and  Other  Signals. —  "Whenever  you  see  a  red  flag  with 
a  black  center  expect  a  storm.  The  triangular  pennants  tell 
which  way  the  wind  will  blow.  (See  the  titles  to  the  cuts.)  A 


N.E. 


S.E. 


N.W. 


s.w. 


FIG.  155.     UNITED  STATES  WEATHER  BUREAU  STORM  SIGNALS 

square  white  flag  predicts  fair  weather ;  a  square  blue  flag  pre- 
dicts rain  or  snow ;  a  flag  half  white  and  half  blue  predicts 
local  rain  or  snow  storms.  A  square  white  flag  with  a  black 
center  indicates  that  a  cold  wave  is  to  arrive.  If  the  black 
pennant  (No.  4)  is  hoisted  above  any  flag,  it  means  that  the 
weather  is  going  to  be  warmer.  If  it  is  hoisted  below  any  flag, 
it  means  that  the  weather  is  going  to  be  colder.3 

1  See  Book  II  (Physics),  page  87.  2  Ibid.,  page  88. 

3  These  flags  are  displayed  in  all  towns  where  there  is  an  observing  station  of 
the  United  States  Weather  Bureau,  and  children  who  live  in  such  towns  should 
learn  them  by  heart. 


FIG.  156.     HURRICANE  SIGNAL 


Great  Lakes 


On  the  coast 


Easterly  winds       Westerly  winds 

FIG.  157.     INFORMATION  SIGNALS 

On  the  Great  Lakes  a  red  pennant  denotes  easterly,  a  white  pennant  westerly,  winds. 
A  red  pennant  at  seacoast  stations  indicates  a  storm. 


No.  i,  a  square 
white  flag 


Fair  weather 


No.  2,  a  square 
blue  flag 


Rain  or  snow 


No.  3,  a  square  flag, 
half  white,  half  blue 


Local  rain  or  snow 


No.  4,  a  triangular 
black  pennant 


No.  5,  a  white  flag 
with  a  black  center 


Temperature  Cold  wave 

FIG.  158.     WEATHER  SIGNALS 

By  a  cold  wave  is  meant  a  fall  of  temperature  of  at  least  20°  in  twenty-four  hours. 
N.B.  —  In  all  the  foregoing  pictures  a  red  flag  is  marked  by  vertical  lines;  a  blue  flag 
by  horizontal  lines. 

177 


1 78  THE  SCIENCES 

"  In  some  regions  the  Weather  Bureau  signals  are  given  by 
steam  whistles.  A  long  blast  is  sounded  to  attract  attention, 
then  follow  the  signals  for  weather,  and  next  those  for  temper- 
ature. The  signals  for  weather  are  long  blasts  ;  those  for 
temperature  are  shorter. 

"  One  long  blast  means  '  expect  fair  weather.' 
Two  long  blasts  mean  '  expect  rain  or  snow.' 
Three  long  blasts  mean  « expect  local  rains  or  snows.' 

"  One  short  blast  means  '  expect  lower  temperature.' 
Two  short  blasts  mean  '  expect  higher  temperature.' 
Three  short  blasts  mean  « expect  a  cold  wave.' 

"  You  have  no  idea  how  useful  these  weather  predictions 
are  nor  how  many  people  read  them  and  follow  their  indica- 
tions. Think, about  it  a  moment.  Suppose  there  is  a  cold 
wave  far  up  in  Winnipeg  moving  eastward.  Often  it  makes 
cold  north  winds  in  Texas  —  a  *  norther  '  —  and  northers  are 
destructive  to  crops  and  to  cattle.  The  whole  of  the  United 
States  from  the  Mississippi  River  eastward  to  Maine  and  south- 
ward to  Florida  is  going  to  feel  it,  and  every  one  is  warned  to 
get  ready.  The  railway  people  are  all  ready  with  snowplows ; 
stock  raisers  herd  their  cattle  into  shelters  and  provide  food  for 
them  ;  people  who  are  shipping  fruit,  etc.,  on  trains  take  warning 
and  wait ;  orange  growers  in  Florida  light  fires  to  protect  their 
trees ;  ice  companies  prepare  to  get  in  their  crop  of  ice ;  house- 
holders see  that  there  is  plenty  of  coal  for  their  furnaces ;  fire- 
men take  extra  precautions  about  their  hydrants.  There  are 
millions  of  people  who  are  affected  in  thousands  of  ways.  The 
government  Weather  Bureau  warns  them  all,  and  every  man 
must  look  out  for  himself  and  for  his  business.  That  is  the 
way  a  government  like  ours  should  be,  I  think.  It  ought  to  do 


friijffUfl 
[pf*|ilr 

r  -w  HE.?!  -- 


S-  2^  3*  3 

i||i 

^33" 


i79 


i8o 


THE   SCIENCES 


the  things  that  no  single  man  can  do  —  like  this  weather  pre- 
diction —  and  leave  every  man  to  take  care  of  his  own  affairs 
afterwards." 

Lightning.  —  "  The  clouds  in  storms  are  electrified,"  said  Jack, 
"and  lightning  is  electric  sparks  on  a  large  scale  exchanged 


FIG.  160.     THUNDER  SQUALLS 

A  part  of  the  preceding  picture  (within  the  space  marked  d  b  q  in  Fig.  159)  is  drawn  on  a 
larger  scale  here.  The  first  picture  shows  the  thunderstorm  as  it  moves  across  the 
country  at  the  rate  of  twenty  to  fifty  miles  an  hour.  This  picture  shows  the  thunder 
squall  as  it  reaches  any  particular  place.  The  arrows  indicate  how  the  different  winds 
are  blowing.  If  the  two  pictures  are  carefully  studied,  and  especially  if  the  reader  will 
compare  them  with  the  summer  thunderstorms  seen  at  his  own  home,  they  will  explain 
most  of  the  appearances  he  sees. 

between  one  cloud  and  another.  Thunder  is  the  crackle  of  the 
spark  echoed  among  the  clouds  and  mountains.  Sheet  light- 
ning is  usually  the  reflection  of  distant  forked  lightning  from 
the  surface  of  high  clouds." 


METEOROLOGY 


181 


Agnes.    Thunder  is  the  echo  that  we  hear,  and  sheet  lightning 
is  a  kind  of  echo  that  we  see. 

Tom.    How  fast  does  lightning  travel,  Jack  ? 

Jack.  Exactly  as  fast  as  light  does — at  the  rate  of  186,000 
miles  in  a  second — so  that  the  duration  of  a  lightning  flash  is 
only  a  very  small  fraction  of 
a  second.  After  the  flash 
comes  the  thunder.  Do  you 
know  how  to  tell  how  far 
away  a  thunderstorm  is? 

Distance  of  a  Thunderstorm 
from  the  Observer.  --  Tom. 
You  notice  the  flash  of  light- 
ning and  then  count  the  num- 
ber of  seconds  till  you  hear 
the  thunder  ;  I  know  that 
much,  but  I  forget  the  rest. 

Jack.  It 's  like  this.  The 
lightning  flash  and  the  thun- 
der occur  in  the  storm  at 
exactly  the  same  moment. 

You  are  far  off  from  it.  You  see  the  flash  the  moment  it  occurs 
because  light  travels  so  fast ;  but  as  sound  travels  only  1 100  feet 
in  a  second,  it  takes  time  for  the  sound  of  the  thunder  to  reach 
you.  You  have  to  multiply  the  number  of  seconds  between 
the  time  of  the  flash  and  the  time  of  the  thunder  by  noo, 
and  you  '11  have  the  distance  of  the  storm  in  feet. 


FIG.  161.     LIGHTNING  FLASHES 


The  sound  of  the  thunder  is      The  storm  is 
heard  after  the  flash  by :  distant  : 


Two  seconds. 
Three     " 


2200  feet. 
3300    « 


The  sound  of  the  thunder  is 
heard  after  the  flash  by  : 

Four  seconds. 
Five        " 


The  storm  is 
distant : 

4400  feet. 

5500    "  (about  a  mile). 


It  takes  sound  about  five  seconds  to  travel  a  mile. 


1 82  THE   SCIENCES 

Lightning  Rods.  — "  Some    people    say,"    said    Fred,    "that 
lightning  rods  aren't  of  any  use.     How  is  it,  Jack?" 

Jack.  Well,  no  lightning  rods  are  so  good  that  you  can  be 
certain  your  house  will  not  be  struck.  The  government  takes 
the  greatest  pains  to  protect  its  powder  magazines,  but  once  in 
a  while  they  are  struck.  Still,  a  lightning  rod  really  does 
protect.  It  should  be  a  good-sized  copper  rod  that  goes  deep 
down  into  the  ground — far  enough  to  reach  moist  earth— 
and  it  should  extend  ten  or  twelve  feet  above  the  roof,  and  end 
in  a  sharp  point.  Three  or  four  good  rods  will  protect  an 
ordinary  house  almost  always.  It  is  better  to  have  them  ;  you 
are  safer. 


i84 


BOOK   V 


PHYSIOGRAPHY 

THE   SCIENCE  OF   THE  LAND   AND   OF  THE   SEA 

The  Oceans.  —  The  children  were  looking  at  a  large  globe 
and  talking  about  it.  First  they  turned  it  so  as  to  show  the 
water  hemisphere,  then  so  as  to  show  the  land  hemisphere, 
and  then  so  as  to  show  the  two  poles — arctic  and  antarctic. 
(See  the  pictures,  Figs.  6  and  7.) 

Mary.  I  never  quite  understood  before  how  much  sea  there 
was  and  how  very  little  land. 

Tom.  The  books  say  that  three  quarters  of  the  surface  of 
the  earth  are  water,  and  this  globe  makes  you  believe  it. 

"  You  'd  believe  it,  if  you  ever  made  a  long  voyage  by  sea," 
said  Tom's  father.  "  Once  I  sailed  straight  west  for  a  whole 
month  in  the  Pacific,  from  Peru  to  Tahiti,  and  at  the  end  of  the 
month  I  was  only  halfway  across  to  Australia.  I  knew  all  about 
maps  and  globes,  but  I  never  realized  how  large  the  Pacific  was 
until  that  time.  I  've  had  a  respect  for  the  mere  size  of  it 
ever  since." 

Tom.  The  Atlantic  is  large,  too,  but  we  don't  think  of 
it  as  so  very  large  because  the  steamers  to  England  are 
so  very  swift.  They  cross  from  New  York  to  Liverpool  in 
six  days. 

185 


i86 


THE   SCIENCES 


Jack.    There  's  another  thing.     The  Atlantic  has  cables  across 
it  in  many  places  and  we  read  the  telegrams  from  Europe  in 
the  newspapers  every  day.     That  makes  England  seem  near. 
Mary.    How  deep  is  the  sea,  Jack  ? 

Jack.  Oh,  it  is  of  very  different  depths  in  different  places. 
The  Atlantic  Ocean,  on  the  average,  is  a  little  over  two  miles, 
and  the  Pacific  is  deeper  —  about  three  miles.  But  you  know 
there  are  places  where  the  sea  is  much 
deeper  —  nearly  six  miles.  Near  our  new 
island  of  Guam  in  the  Pacific  there  is  a 
spot  31,600  feet  deep. 

Fred.  The  highest  mountains  are  about 
five  miles  ;  the  sea  is  as  deep  as  the  moun- 
tains are  high.  That  is  a  way  to  remember. 
Jack.  Yes  ;  but  you  must  remember, 
too,  that  there  is  very  much  more  area  of 
deep  sea  than  of  mountain  regions,  so  you 
could  not  fill  up  the  sea  by  putting  the 
mountains  in  it.  You  would  have  to 
borrow  some  land  from  another  planet 
to  fill  it  up. 

Depth  of  the  Sea —  "  I  suppose  they 
find  the  depth  of  the  sea  by  sounding  with 
a  weight  on  the  end  of  a  rope,  don't  they  ? 
—  just  as  we  do  in  a  pond,"  said  Fred. 

Tom.    They  do  not  use  rope ;  they  use 
piano  wire ;  the  rope  would  float  —  or  at 
least  it  would  not  sink  as  quickly  as  wire  does. 

Jack.  Yes,  they  use  miles  of  fine  piano  wire  and  a  heavy 
weight  that  drops  off  when  it  strikes  the  bottom.  That  makes 
it  easy  to  reel  the  wire  in  again. 


FIG.  163.     A  DEEP- 
SEA  DREDGE 

It  is  a  large  bag  or  scoop 
for  bringing  up  parts  of 
the  ocean  floor.  Little 
shells  and  so  forth  are 
caught  by  the  tassels. 


PHYSIOGRAPHY 


I87 


Agnes.  What  is  at  the  bottom  of 
the  sea,  Jack  ? 

Jack.  Anywhere  near  the  land 
the  sea  bottom  is  covered  with  mud. 
The  rivers  and  the  rains  carry  the 
soil  of  the  land  far  out  to  sea  and 
the  ocean  floor  is  covered  with  it. 

Little  pieces  of  the  rocks  of  the 
land  are  carried  out  to  sea,  and  you 
find  the  same  rocks  in  this  mud  that 
we  have  on  the  land.  The  Missis- 
sippi or  the  Amazon  river  carries 
its  mud  out  to  sea  for  hundreds  of 
miles.  When  you  get  very  far  from 
land  the  dredge  brings  up  a  differ- 
ent kind  of  rock.  The  little  pieces 
of  rock  in  the  sea  bottom  very  far 
from  land  have  sharp  angles.  They 
have  not  been  rolled  about  by  surf 
and  their  corners  are  sharp  like 
crystals. 

Besides  these  rocks  the  dredge 
brings  up  the  shells  of  little  creatures 
that  live  near  the  surface  of  the  sea. 
When  they  die  their  shells  sink  to 
the  bottom,  and  there  are  millions 
and  millions  of  them,  so  that  a  good 
part  of  the  ocean  floor  is  covered 
with  a  kind  of  ooze  —  they  call  it — 
mostly  made  of  these  shells.  Then 
we  find  the  bones  of  fishes,  the  teeth 


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« 

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n£M4 


FIG.  164 

A  bit  of  the  ocean  floor  from  a  region 
within  a  few  hundred  miles  of  the 
land.  Notice  that  the  fragments  of 
rock  are  rounded,  which  shows  that 
they  have  been  washed  by  waves. 


%&.»mm$ 

.  ^  n    v      M.          .jf^3  o  /^      «K          '         i 


FIG.  165 

A  bit  of  the  red  clay  of  the  floor  of 
the  deep  ocean  far  from  shore. 
Notice  that  the  fragments  of  the 
rock  have  sharp  angles,  which 
proves  that  they  have  not  been 
rolled  about  by  surf  and  do  not 
come  from  the  washings  of  the 
continents. 


1 88 


THE  SCIENCES 


of  sharks,  and  things  of  that  kind  imbedded  in  the  clay ;  and 
small  pieces  of  ivory,  too,  with  pieces  of  meteors  which  have 
fallen  into  the  sea.  You  see  the  ocean  floor  is  made  up  of  at 
least  three  different  things  —  the  washings  of  the  continents, 
the  red  clay,  and  the  ooze  of  shells  and  the  like. 

Tom.  Then,  of  course,  the 
ocean  is  full  of  fish. 

Jack.  There  are  plenty  of 
fish  near  the  surface.  They 
live  where  their  food  is,  and 
most  of  it  is  near  the  surface. 
There  are  some  fish  in  the 
greatest  depths,  too,  but  the 
living  things  there  are  mostly 
crabs,  starfish,  shellfish,  and 
so  forth.  You  know  the  sur- 
face of  the  water  is  crowded 
with  jellyfish  of  all  kinds. 

The  jellyfish  are  phosphor- 
escent. They  glow  when  they 
are  disturbed  just  as  a  sulphur 


FIG.  1 66.     A  FLOATING  JELLYFISH 


match  glows  when  you  rub  it 
All  the  light  at  the  bottom  of 
The  sunlight  does  not  go  very 


with  your  fingers  in  the  dark. 
the  sea  comes  from  jellyfish. 
deep  down. 

Tom.    How  do  you  know  there  is  any  light  at  the  bottom  of 
the  sea,  then  ? 

Jack.  Because  the  deep-sea  fish  have  eyes.  If  there  were 
no  light  whatever,  all  the  fish  would,  in  time,  lose  their  eyes, 
just  as  the  fish  in  the  Mammoth  Cave  have ;  but  many  of  the 
deep-sea  fish  have  eyes. 


PHYSIOGRAPHY 


189 


Fred.  There  are  fish  —  whales  and  so  forth  —  near  the  sur- 
face of  the  sea ;  and  there  are  starfish  and  crabs  and  shellfish 
at  the  bottom.  What  is  in  between? 

Jack.  Almost  nothing,  Fred;  just  dark,  quiet,  cold  water, 
with  no  seaweed,  no  plants,  no  animals,  and  no  fish.  There  is 
no  life  there  to  speak  of  ;  no  light  and  no  motion,  for  the 
waves  that  we  see  on  the  surface  do  not  go  down  very  deep 
either.  The  middle  depths  of  the  ocean  are  the  most  dreary 


FIG..  167.    A  DEEP-SEA  FISH  WITH  EYES 


FIG.  1 68.     A  DEEP-SEA  SPIRULA,  A  KIND  OF  CUTTLEFISH 
The  real  fish  is  just  twice  the  size  of  the  picture. 

and  the  most  monotonous  places  you  can  conceive  of.  The 
arctic  regions  are  gay  compared  to  them  ! 

Icebergs.  — "  How  do  you  children  suppose  an  iceberg  is 
formed  ?  "  said  Jack. 

Mary.    I  suppose  the  sea  water  freezes  and  makes  it. 

Fred.  That  will  not  do,  Mary.  Don't  you  see  that  water 
could  not  freeze  high  up  in  the  air  like  that  ? 

Jack.    Do  any  of  you  know  ? 

Tom.    Icebergs  break  off  from  the  ends  of  glaciers,  they  say. 


FIG.  169.     A  FLOATING  ICEBERG 

Ice  is  a  little  lighter  than  water  and  it  floats,  therefore.    About  one  seventh  of  an 
iceberg' shows  above  the  surface ;  six  sevenths  are  below. 


FIG.  170.    ICEBERGS  BREAKING  OFF  FROM  THE  END  OF  MUIR  GLACIER 

IN  ALASKA 
190 


PHYSIOGRAPHY 


IQI 


Glaciers.  —  "And  glaciers  are  rivers  of  ice  flowing  slowly 
down  from  the  mountains,"  said  Jack. 

Agnes.    Do  they  flow  like  rivers  ? 

Jack.  They  flow  somewhat  as  rivers  do ;  yes,  only  very 
much  slower  —  a  few  hundred  feet  a  year,  for  instance ;  but 
they  often  keep  on  till  they  reach  the  sea  (see  Fig.  170),  and 
there  huge  pieces  break 
off  and  form  bergs. 

Tom.  Then  the  water 
of  icebergs  is  not  salt ;  it 
is  fresh. 

Jack.  Yes,  it  is  rain 
water  that  has  fallen  as 
snow,  you  see. 

Mary.  But  the  sea 
water  does  freeze,  Jack, 
does  n't  it  ? 

Jack.  Certainly  ;  and  makes  the  great  ice  fields  that  you  have 
read  about. 

Some  of  these  fields  are  very  thick,  especially  when  they 
have  been  packed  together  by  tides  and  currents.  When  the 
ice  first  freezes  it  is  smooth,  of  course,  but  after  it  has  been 
packed  it  is  horribly  rough.  It  is  often  entirely  too  rough  to 
travel  over,  and  that  is  the  reason  why  it  is  so  hard  to  get 
to  the  north  pole. 

Tom.  You  go  as  far  as  you  can  in  your  ship,  and  then  you 
take  dog  sledges,  and  finally  you  come  to  ice  too  rough  to  travel 
over.  Is  that  it? 

Jack.  Yes ;  the  ice  blocks  are  as  big  as  houses  and  are 
all  piled  together  every  which  way,  and  a  day's  journey  is  often 
only  three  or  four  miles. 


FIG.  171.     A  BOWLDER  OF  ROCK  THAT  WAS 

ONCE   ON   THE   TOP   OF  A   GLACIER 

The  glacier  brought  it  from  far  away,  and  the  rock 
was  left  here  when  the  glacier  melted. 


FIG.  172.    A  ROCK  ON  THE  COAST  OF  MAINE  THAT  WAS  ONCE  UNDER  A 
GLACIER  AND  HAS  BEEN  WORN  SMOOTH  BY  THE  ICE 


FIG.  173.     THE  BEGINNING  OF  A  GLACIER  HIGH  UP  IN  THE  MOUNTAINS 

The  snow  of  the  peaks  slides  into  and  down  the  valleys  and  becomes  ice  by  the  pressure  of  the 
tightly  packed  mass.     If  you  pack  a  snowball  very  tight,  it  becomes  nearly  pure  ice. 

192 


PHYSIOGRAPHY 


193 


Rivers  and  Streams.  —  "  Did  you  children  ever  think  of  how 
a  drop  of  rain  water  gets  from  the  mountains  into  the  sea?" 
said  Jack.  "  It  is  worth  while.  Suppose  you  begin  by  thinking 
of  what  happens  when  the  rain  falls  on  a  plowed  field.  The 


FIG.  174.     A  SHIP  FROZEN  IN  AN  ICE  FIELD 

next  time  there  is  a  rain  you  must  look  carefully  and  see 
exactly  what  takes  place." 

Underground  Water.  — "  Part  of  the  water  soaks  into  the 
ground,  but  most  of  it  runs  off  in  little  streams,"  said  Tom. 

Jack.  What  becomes  of  the  water  that  soaks  into  the  ground, 
Agnes  ? 

Agnes.  Why,  a  good  deal  of  it  stays  there.  If  you  dig  down, 
the  ground  is  always  moist. 

Jack.  And  when  corn  is  planted  in  the  field  it  gets  a  good 
part  of  its  water  from  the  earth.  You  know  there  is  a  great  deal 
of  water  in  Indian  corn  —  in  the  ears  and  in  the  stalks  ;  so 
some  of  last  month's  rain  will  be  in  the  sweet  corn  you  will  eat 


194 


THE  SCIENCES 


next  August.  Now,  what  becomes  of  the  water  that  does  not 
get  into  the  ground  but  runs  off  ? 

Fred.  Some  of  it  gets  into  the  air  as  moisture  and  makes 
fog  and  clouds. 

Agnes.    Yes,  and  those  clouds  may  bring  rain  again. 

Mary.  But  not  on  our  field  ;  they  will  be  far  away  the  next 
time  it  rains. 

Fred.  And  most  of  the  water  runs  off  in  little  streams  and 
by  and  by  gets  into  the  brook. 

Mary.  And  the  brook  carries  it  off  to  the  river,  and  the 
river  to  another  river,  and  so  on,  till  it  gets  to  the  sea. 


FIG.  175. 


LITTLE  STREAMLETS  OF  RAIN  WATER  RUNNING  OFF 
PLOWED  GROUND 


Jack.    Does  the  water  ever  flow  uphill  ? 

Agnes.    No,  of  course  not. 

Jack.  Then  it  is  downhill  all  the  way  from  our  field  to  the 
sea.  If  you  followed  a  drop  of  water  in  the  brook,  it  would 
always  be  traveling  downhill,  but  it  would  not  go  straight. 

Fred.    I  should  think  not !     No  rivers  are  straight. 

Jack.  A  river  in  Asia  Minor,  called  the  Maeander,  was  so  full 
of  bends  that  it  gave  a  name  to  that  habit  of  rivers ;  we  call 
them  meandering  rivers,  and  the  bends  meanders. 


PHYSIOGRAPHY 


195 


Agnes.    Can  you  say  that  rivers  have  habits,  Jack  ? 

Jack.  Why  certainly,  Agnes ;  a  habit  is  a  custom,  that  is  all. 
It  is  a  habit  of  rivers  to  flow  downhill,  to  be  crooked,  to  carry 
little  particles  of  sand  and  soil  in  their  streams,  to  roll  pebbles 


FIG.  176.    A  MEANDERING  BROOK 

and  stones  along  their  beds,  and  so  on ;  it  is  a  habit  of  rivers 
to  work  —  they  are  industrious. 

Agnes.    Oh,  Jack  —  industrious  ! 

Tom.  Well,  they  are.  They  carry  no  end  of  soil  and  rocks 
along  in  their  course,  and  they  work  day  and  night,  too. 

Jack.  You  might  almost  think  a  river  was  alive  if  you 
counted  up  all  the  different  things  it  did,  and  you  might 
almost  say  a  river  had  a  purpose  in  life,  just  as  a  man  has. 


196 


THE  SCIENCES 


(See  the  picture  on  page  184.) 


NORTH         CAROLINA  __, / 


Take  the  Colorado  River,  for  instance ;  its  purpose  is  to  get 
to  the  sea  in  the  best  way  possible,  and  it  has  industriously  cut 
a  way  through  rocks  till  its  canon  is  nearly  a  mile  deep. 

Some  rivers  actually  steal. 

Agnes.    Oh,  Jack  !  what  do 
they  steal  ? 

Jack.  Well,  for  one  thing, 
they  steal  water  from  other 
rivers  and  carry  it  away  them- 
selves. For  instance,  the 
Savannah  River  has  stolen  a 
lot  of  branches  from  the  Chat- 
tahoochee. (See  Fig.  177.) 
Then  rivers  are  young  and 
middle  aged  and  old,  too ; 
FIG.  177  torrents  first,  and  then 

The  Chattahoochee  River  formerly  owned  the  Steady-going,  and  by  and  by 
waters  quite  up  to  the  border  of  North  Caro-  Very  mild  and  gentle  J  and 
Una  that  now  flow  in  the  Chateuea  and  Tuea-  •  i  ,  ,-\ 

you  might  say  they  are  angry 

loo  basins  into  the  Savannah  River  and  so  to  J  •>  &   J 

the  sea.     It  is  quite  likely  that  the  Oconee  when  they  are  in  flood.       The 

River  will  capture  more  of  the  Chattahoochee  Yellow     River    in     China    has 
waters  in  times  to  come. 

drowned  a  million  persons  in 

a  year  (1887);  the  Ganges  is  nearly  as  bad;  and  our  own 
Mississippi  has  terrible  floods. 

Fred.  Anyhow  they  don't  mean  any  harm,  and  they  are 
industrious  ;  they  do  the  best  they  know  how. 

Jack.  Industrious  they  certainly  are.  In  the  first  place,  the 
water  dissolves  a  great  deal  of  rocky  soil  (just  as  water  dissolves 
sugar)  and  carries  it  along  to  a  new  place.  Then  a  river  carries 
a  great  deal  of  sand  and  mud  in  its  stream,  and  drops  that,  too, 
when  it  can  carry  it  no  longer. 


PHYSIOGRAPHY 


197 


Agnes.    When  does  it  drop  the  mud,  Jack;  when  it  gets  tired  ? 

Jack.  You  might  say  so.  While  the  river  is  flowing  fast  it 
can  carry  a  great  deal  of  mud  and  sand ;  as  soon  as  it  begins 
to  move  slower  some  of  this  mud  falls  to  the  bottom. 

Tom.    If  you  want  to  get  dirt  out  of  a  wash  basin,  you  have 


FIG.  178.     THE  TOWN  OF  EMS  (PRUSSIA)  BUILT  ON  THE  NARROW 
FLOOD  PLAIN  OF  THE  LAHN  RIVER 

to  make  the  water  move  quickly.     If  it  moves  slowly,  the  dirt 
begins  to  settle. 

Jack.  They  say  that  the  Mississippi  carries  mud  enough  every 
year  to  make  a  range  of  hills  a  mile  long,  half  a  mile  wide  at 
the  bottom,  and  five  hundred  feet  high;  and  the  Nile  brings 
huge  quantities  of  soil  into  lower  Egypt.  The  flood  plains  of 
such  rivers  are  the  most  fertile  parts  of  the  world. 


I98 


PHYSIOGRAPHY 


199 


The  Land.  —  "When  people  talk  about  the  sea,"  said  Jack, 
"  they  speak  about  it  as  if  it  were  always  changing —  they  call  it 
*  the  restless  sea  ' ;  and  when  they  talk  about  the  land  they 
speak  as  if  the  land  never  changed  at  all  —  *  the  everlasting 
hills,'  they  say.  Of  course  it  is  true  that  the  hills  and  moun- 
tains do  not  change  much  in  your  lifetime  or  in  mine,  and  of 


FIG.  180.     A  MOUNTAIN  RANGE  IN  CALIFORNIA 

The  summits  are  covered  with  snow  which,  melting,  forms  the  brooks  and  rivers  ;  rains  model 
the  ravines.     Every  feature  of  this  landscape  has  been  formed  by  running  water. 

course  it 's  true  that  if  you  are  at  the  seashore  the  waves  are 
never  still  for  a  moment ;  but  really  and  truly  the  land  changes 
more  than  the  sea  does,  if  you  take  the  whole  history  of  it. 
The  surface  of  the  land  is  changing  all  the  time." 

Mary.    I  don't  quite  see  how,  Jack.      I  have  been  here  all 
summer.     What  changes  have  there  been? 


200  THE  SCIENCES 

Jack.  You  have  seen  the  brook  to-day.  What  color  was  the 
water,  Mary  ? 

Mary.    Why,  it  was  clear. 

Jack.  And  yesterday,  when  it  was  raining  so  hard,  what  color 
was  it  ? 

Mary.  It  was  muddy.  Yes,  I  see;  the  rain  from  the  ground 
carried  off  some  of  the  soil  to  the  brook.  It  was  not  much, 
though. 

Jack.  No,  not  much.  But  suppose  you  have  a  hundred 
showers  every  year;  in  a  hundred  years  there  will  be  ten  thou- 
sand showers,  and  every  shower  will  do  some  work  and  will  carry 
away  some  soil.  In  a  hundred  centuries  there  will  be  a  million 


FIG.  181.     SAND  MOUNTAINS  (DUNES)  IN  THE  RAINLESS  DESERT  OF 
THE  SAHARA 

They  are  modeled  by  the  wind.     Along  many  seacoasts  such  dunes  are  to  be  found. 

showers  ;  every  one  of  them  will  do  some  work,  and  all  of 
them  together  will  do  a  great  deal.  They  will  sculpture 
mountains  and  level  continents. 

Mountains.  —  "Nearly  all  the  mountains  of  the  globe  are 
modeled  by  water.  Wherever  there  is  frost,  too,  great  pieces 
of  rock  break  off  and  fall.  The  shapes  of  mountains  in  arid 
countries  like  Arizona  are  modeled  by  the  winds ;  and  then, 


PHYSIOGRAPHY 


2OI 


you  know,  there  are  volcanoes,  and  they  change  their  shape, 
too.     Everywhere  the  form  of  the  land  is  changing." 

Tom.    If  all  this  went  on  long  enough,  the  earth  would  be  flat. 

Agnes.  You  might  say  more  than  that,  Tom.  You  might 
say  that  the  rains  would 
make  all  the  mountains  flat, 
and  that  the  rivers  would 
carry  everything  to  the  sea. 
Why  does  n't  that  happen, 
Jack?  Why  isn't  all  the 
land  carried  into  the  ocean  ? 
Why  is  n't  the  whole  world 
flat? 

Jack.  If  you  gave  it  time 
enough,  it  would  be,  Agnes  ; 
but  it  would  take  a  great 
deal  of  time !  The  books 
say  that  the  surface  of  a 
whole  continent  might  be 
lowered  an  inch  or  so  in  a 
century.  North  America 
is,  on  the  average,  about 

2000  feet  (that  is  24,000  inches)  above  the  ocean,  so  you 
see  that  it  would  take  at  least  24,000  centuries  to  level  it  — 
at  least  2,400,000  years.  But  long  before  that  time  other 
things  would  happen  to  prevent.  Some  of  the  continents 
are  slowly  rising  out  of  the  sea  all  the  time,  and  it  is  the 
elevation  of  whole  countries  that  makes  up  for  the  washing 
away  of  the  land. 

Tom.    I  never  heard  of  that  before,  and  I  don't  understand 
it.     What  countries  are  rising  now,  for  instance  ? 


FIG.  182.     A  CLIFF  OF  HARD  ROCK 

The  sloping  bank  at  its  foot  is  made  up  of  rock 
that  has  fallen  from  the  cliff. 


2O2 


THE    SCIENCES 


Jack.   Well  —  Sweden  is  rising,  slowly  rising,  two  or  three  feet 

in  a  century.    And  the  northern  coast  of  California  is  rising,  and 

many  other  coasts  and  regions,  too.     They  say  the  coasts  of 

Alaska  and  of  Peru  have  been  raised  more  than  a  thousand  feet. 

Agnes.    Aren't  some  regions  sinking? 

Jack.    Yes,  of  course.     If  one  region  rises,  others  will  sink. 
They  say  the  coasts  of  Massachusetts  and  of  New  Jersey  are 

now  sinking  about 
two  feet  in  a  hundred 
years;  and  there  are 
plenty  of  other  places, 
too,  but  I  don't  re- 
member them  now. 
Agnes.  But,  Jack, 
how  can  people  pos- 
sibly know  that  a 
country  is  sinking,  if 
it  moves  as  slowly  as 
that  ?  Two  feet  in 
a  hundred  years  — 
why,  how  can  they 
tell  ? 

Jack.  Well,  it  is  not  easy,  but  there  are  ways  to  do  it.  If 
the  sinking  keeps  on  long  enough,  it  is  not  hard  to  observe  it. 
For  instance,  there  is  a  part  of  the  German  Ocean  not  far  from 
the  mouth  of  the  Thames  where  the  whole  coast  has  sunk. 
They  say  you  can  even  see  the  remains  of  buildings  at  the 
bottom  of  the  sea  when  the  water  is  clear.  Those  were 
English  cities,  and  the  land  has  sunk  within  a  few  hundred 
years.  We  know  the  history  of  it,  I  believe.  There  is  a  very 
good  way  to  tell,  though,  what  land  has  risen  out  of  the  ocean. 


FIG.  183.     FOSSIL  SHELLS  IMBEDDED 
IN  LIMESTONE 


PHYSIOGRAPHY 


203 


Tom.    What  way,  Jack  ? 

Jack.  By  seashells  - —  fossil  seashells  — found  on  land,  even  on 
mountain  tops.  Suppose  you  should  find,  not  one,  but  thousands 
and  thousands  of  seashells  on  the  very  top  of  a  hill ;  suppose  that 
the  whole  rock  should  be  made  of  them.  Well,  would  n't  that 
prove  that  that  particular  hill  had  once  been  under  the  sea  ? 
Tom.  Yes,  you  could  prove  it  that  way. 

Jack.    Now  suppose  that  all  the  hills  for  hundreds  of  miles 
around  were  made  of  shells — of  shells  of  animals  that  we  know 


FIG.  184.    THE  UPLAND  OF  NEW  ENGLAND  WITH  MOUNT  MONADNOCK 
IN  THE  DISTANCE 

cannot  live  on  land,  but  absolutely  must  live  in  salt  water — 
would  not  that  prove  that  the  region  had  been  under  salt  water 
long  ago  ? 

Tom.    Yes,  of  course.     Are  there  many  regions  like  that? 
Jack.    Hundreds  of  them.      And  in  some  of  them  every  bit 
of  the  rock  is  filled  with  seashells.     You  know  what  sandstone 
is,  of  course  ? 


204 


THE  SCIENCES 


Tom.    Yes,  there  is  a  lot  of  it  here.     Some  of  our  hills  are 
all  sandstone. 

Jack.  Well,  sandstone  is  nothing  but  little  grains  of  sand 
cemented  together  to  make  rock;  and  many  sandstones  have 
been  formed  under  water  —  under  salt  water.  A  large  river, 
let  us  say,  brings  sand  from  the  shore,  and  drops  the  sand 


FIG.  185.    A  MOUNTAIN  IN  UTAH  FILLED  WITH  RAVINES,  EVERY  ONE  OF 

WHICH    HAS    BEEN    MODELED    BY    RUNNING    WATER 


grains  on  the  sea  bottom.  In  time  the  grains  are  cemented 
together,  and  then  you  have  layers  of  sandstone.  By  and  by 
something  like  a  great  slow  earthquake  happens,  and  the  sand- 
stone is  lifted  above  the  sea.  It  may  be  lifted,  in  time,  very 
high.  Then  you  have  layers  of  sandstone  on  land.  The  rains 
come  and  wear  it  into  ravines,  and  parts  of  it  crack  and  fall,  and 
some  of  it  is  covered  with  soil  by  the  washings  of  other  rivers, 


PHYSIOGRAPHY 


205 


and  by  and  by  trees  and  grass  grow  there,  and  you  have  a 
country  like  the  one  we  live  in. 

The  earth  is  not  solid  down  to  its  center,  you  know.  We 
live  on  the  outside  crust  of  it.  That  is  solid,  of  course,  and 
it  is  about  a  hundred  miles  thick.  Inside  of  that  crust  great 
parts  of  the  globe  are  red-hot  rocks,  like  melted  lava.  It  is  as 
if  the  continents  and  the  oceans  were  resting  on  an  inside  globe 
of  melted  rock.  The  heaviest  parts  are  always  pressing  down, 
and  the  crust  is  always  being  strained 
and  bent  and  cracked.  Some  parts 
of  the  earth  are  sinking  very  slowly, 
and  other  parts  are  slowly  rising. 
Wherever  the  crust  moves  you  have 
cracks,  and  when  the  cracks  are  large 
you  have  long  valleys  and  mountain 
ridges.  (See  the  picture,  Fig.  188.) 

Stratified  Rocks.  —  "  Are  all  moun- 
tains made  in  that  way,  Jack  ? "  said 
Tom. 

Jack.  Not  exactly  in  that  way,  Tom. 
You  see  it  is  like  this  :  The  crust  of 
the  earth  sometimes  breaks  one  way, 
and  you  have  mountains  like  those  in 
the  picture  (Fig.  188) ;  and  sometimes 
it  does  not  break  at  all,  but  bends ;  it  may  be  pressed  or 
crumpled  so  slowly  that  it  can  yield  without  much  breaking. 
There  is  a  way  to  prove  this.  Do  you  know  what  stratified 
rock  is  ? 

Tom.    It  is  rock  in  layers  —  in  strata. 

Jack.    Yes.     Now  we  know  that  those  layers  were,  in  the  first 
place,  horizontal.     They  were  layers  of  sand  on  the  bottom  of  the 


FIG.  1 86 

The  earth's  solid  crust  is  about 
100  miles  thick  ;  the  narrow  line 
in  the  picture  would  be  more 
than  100  miles  thick  if  the  diam- 
eter of  the  circle  were  8000 
miles.  Within  the  crust  the 
rocks  are  very  hot  —  melted. 
The  pressures  in  the  interior  are 
so  great  that  the  rocks,  though 
melted,  do  not  flow  like  a  liquid, 
but  are  almost  rigid,  like  a  solid. 


FIG.  187.     MODEL  TO  SHOW  HOW  MOUNTAINS  ARE  MADE  BY  THE 
CRACKING  OF  THE  EARTH'S  CRUST 


FIG.  188.     VIEW  OF  THE  MOUNTAINS  FORMED  BY  THE  CRACKING  OF  THE 
EARTH'S  CRUST.     (SEE  FIG.  187.) 

They  are  in  southern  Oregon  and  northern  Nevada  and  California.     The  long  lakes  and 
the  streams  lie  in  the  direction  of  the  cracks. 


206 


PHYSIOGRAPHY 


207 


sea,  or  perhaps  they  were  layers  of  limestone  with  fossil  shells 
scattered  through  them.     In  the  pictures  (Figs.  182  and  189) 


FIG.  189.     A  COLUMN  OF  STRATIFIED  ROCK 

The  rock  is  made  up  of  nearly  horizontal  layers.  The  softer  rock  between  the  column  and 
the  cliff  has  been  worn  away  by  the  waves  in  the  course  of  thousands  of  years.  Fig.  182, 
preceding,  shows  a  cliff  of  stratified  rock  —  of  rock  arranged  in  layers. 


they  have  been  lifted  up  so  as  to  keep  the  layers  level ;  but 
there  are  places,  many  places,  where  the  layers  have  been 
crumpled  like  this: 
(See  also  Fig.  190.) 


208 


THE   SCIENCES 


The  crumpling  makes  the  crust  into  mountains  and  valleys, 
and  you  must  always  remember  that  just  as  soon  as  a  moun- 
tain is  lifted  up,  it  begins  to  be  torn  down  again  by  the  frosts, 
the  rains,  the  earthquakes.  The  older  the  mountain  is,  the 


FIG.  190 

Strata  once  horizontal  are  sometimes  elevated  and  folded  so  as  to  make  mountain  ranges,  as 
in  the  picture,  which  shows  such  a  case  in  Maryland.  The  Appalachian  ridges  in  Penn- 
sylvania (and  the  Jura  Mountains  in  Switzerland)  were  made  in  this  way. 

more  its  first  shape  has  been  altered,  and  you  can  tell  its  age 
in  that  way.      (See  Figs.  180  and  185.) 

The  oldest  mountains  in  America  are  the  Laurentian  Hills, 
near  the  St.  Lawrence  River,  and  the  Green  and  Adirondack 
mountains.  The  Green  Mountains  are  about  forty  or  fifty 
million  years  old,  the  geologists  say. 


PHYSIOGRAPHY  209 

Fred.    What  are  the  youngest  mountains,  Jack  ? 

Jack.  The  youngest  in  America  are  the  Coast  Ranges  of  the 
Pacific  slope.  The  books  say  they  are  about  two  or  three 
millions  years  old.  Two  million  years  is  young  for  a  moun- 
tain. The  Wasatch  Mountains  in  Utah  are  middle  aged. 

The  Age  of  the  Earth.  —  "  Do  they  know  how  old  the  earth 
is  ?  "  said  Tom. 

Jack.  It  is  not  known  in  the  way  you  can  say  you  know  how 
old  a  tree  is  after  you  have  counted  the  number  of  rings  in  its 
sawed-off  stump ;  but  it  is  known  in  a  way.  Take  these  very 
stratified  rocks,  for  instance.  They  were  formed  under  water 
by  sand  which  settled  down  on  the  ocean  floor  and  slowly 
cemented  into  rock.  A  layer  a  foot  thick  will  be  formed  in 
about  10,000  years,  the  geologists  say.  Then  a  layer  100  feet 
thick  might  be  formed  in  about  a  million  years,  and  a  layer 
ten  miles  thick  in  about  500,000,000  years.  There  is  good 
reason  to  believe  that  the  earth  is  at  least  as  old  as  that,  and 
maybe  older.1 

Agnes.  Five  hundred  million  years  !  I  shall  never  be  able 
to  realize  that  !  Why,  I  can't  even  understand  what  a  million 
years  is. 

Jack.  You  remember  how  you  children  made  a  model  of  the 
solar  system  ? 2  It  helped  you  to  understand  large  numbers, 
did  n't  it  ?  Well,  you  can  do  something  of  the  same  sort  here. 
Suppose  that  the  next  time  you  walk  to  the  village  you  play 
that  every  one  of  your  steps  counts  for  a  year.  When  you 

1  There  is  no  part  of  the  earth  where  we  can  see  horizontal  layers,  one  upon 
another,  ten  miles  thick ;   but  there  are  places  where  the  layers,  once  horizontal 
(  ),  have  been  tilted  up  (//////),  so  that  we  can  now  see  their  ends  and  be 
sure  that  the  original  layers  were  at  least  ten  miles  in  thickness. 

2  See  Book  I  (Astronomy),  page  20. 


210  THE  SCIENCES 

have  taken  125  steps  you  have  gone  back  125  years,  and  that 
will  take  you  back  to  the  time  of  the  Revolutionary  War 
(1901  —  1776=  125);  and  when  you  have  taken  1900  steps  you 
have  gone  back  to  the  time  of  Christ.  When  you  have  walked 
three  miles  you  have  gone  back  to  the  time  when  the  first 
pyramids  were  built.  You  would  have  to  walk  about  twenty 
miles,  each  step  counting  for  a  year,  before  you  got  back  to  the 
time  when  human  beings  first  came  on  the  earth;  and  you  would 
have  to  walk  two  or  three  times  round  the  earth  before  you  got 
back  to  the  time  when  the  first  life  appeared  on  the  earth,  and 
much  farther  yet  to  get  to  the  time  when  the  earth  was  first 
formed. 

Mary.  It  is  puzzling,  but  I  think  I  understand  it  a  little 
better  than  I  did  before. 

Jack.  Well,  my  dear,  suppose  you  remember  what  we  have 
said  and  think  about  it  by  and  by.  Recollect  —  a  step  stands 
for  a  year  ;  you  were  born  twelve  years  ago  —  twelve  steps  just 
takes  you  out  on  to  the  lawn.  The  Pilgrims  landed  281  years 
ago  —  281  steps  down  the  road.  You  can  put  a  peg  here  to 
stand  for  the  coming  of  the  Pilgrims.  Eight  hundred  and 
thirty-five  steps  will  take  you  to  the  landing  of  William  the 
Conqueror  in  England;  put  in  a  peg  for  him.  A  mile  will  take 
you  back  to  600  years  before  Christ ;  the  city  of  Rome  was 
founded  about  that  time.  Two  miles  farther  will  represent 
the  time  when  the  pyramids  were  built  in  Egypt ;  and  when 
you  have  gone  about  twenty  miles  —  a  year  to  each  step  —  you 
will  get  back  to  the  time  that  men  first  appeared  on  the  earth. 
That  is  far  enough  for  now.  The  world  was  a  very  old  world 
when  Man  appeared  on  it ;  it  had  a  long  history  before  he  came. 
There  had  been  life  long  before  his  time,  as  we  know  by  the 
fossils,  —  shells,  fishes,  and  animals  ;  and  there  was  a  long  time, 


PHYSIOGRAPHY  2  1 1 

nobody  knows  how  long,  before  that  when  the  earth  had  no 
life  on  it  at  all — no  men,  no  animals,  not  even  a  plant. 

Age  of  Different  Parts  of  the  Earth.  —  "I  understand  how 
you  can  tell  when  the  oldest  seashells  came,"  said  Tom, 
"because  you  would  find  their  fossils  in  the  oldest  rocks  —  in 
the  rocks  lowest  down ;  and  if  you  find  a  fossil  rhinoceros 
higher  up  in  the  rocks  than  a  fossil  whale,  you  would  say  the 
whale  came  first.  But  how  about  men  ?  Do  they  find  fossil 
skeletons  of  men  ?  " 

Jack.  Sometimes ;  but  more  often  they  find  arrowheads  that 
men  have  chipped  out  of  flint,  along  with  the  fossils  of  animals. 
For  instance,  there  are  caves  where  arrowheads  and  lanceheads 
have  been  found  along  with  the  remains  of  animals,  and  where 
it  is  plain  that  the  caves  were  filled  up  by  some  accident  soon 
after  the  men  had  died  ;  those  men  and  those  animals  lived  at 
the  same  time.  Sometimes  they  find  the  bones  of  the  animals 
split  open,  so  as  to  get  the  marrow  out,  and  blackened 
with  fire. 

Age  of  Man  on  the  Earth.  —  "  Well,  that  would  prove  that 
the  men  used  those  very  animals  for  food,  would  n't  it  ? " 
said  Fred. 

Jack.  Yes,  and  there  is  a  more  wonderful  thing  still.  In  one 
of  the  very  old  caves  they  found  bones  carved  with  pictures  of 
reindeer.  The  man  first  killed  the  reindeer  with  his  arrows, 
and  dragged  him  to  his  cave  and  cooked  him  with  fire.  Then 
there  was  plenty  of  food  in  the  house.  The  man  felt  secure 
and  happy;  he  had  leisure  to  think  and  to  enjoy  himself.  And 
this  drawing  of  a  reindeer  on  a  bone  made  by  a  half-naked 
savage  is  the  beginning  of  all  the  beautiful  pictures  in  the  world. 
The  man  was,  you  may  say,  our  ancestor ;  and  the  drawing  is 
the  ancestor  of  all  the  paintings  of  modern  times. 


212 


THE   SCIENCES 


Tom.    Some  one  ought  to  put  up  a  monument  to  that  man ! 
He  was, the  first  artist  —  long  before  Pheidias  and  the  Greeks. 
Agnes.    How  long  before,  Jack  ? 

Jack.  I  knew  you  were  going  to  ask  me  that,  Agnes.  I 
was  sure  of  it  !  Well,  at  a  guess,  10,000  years  or,  it  may  be, 
1 5,000.  It  is  not  certain,  like  the  date  of  the  last  eclipse,  or  the 
time  when  Rome  was  founded.  It  is  twenty  miles,  Agnes  —  a 
year  to  a  step  —  don't  you  remember  ? 

Agnes.  Yes,  I  remember ;  but  I  don't  see  how  you  can  tell, 
though. 

Tom.     Why,  Agnes,  if  a  man  eats  reindeer  in  order  to  live, 
he  must  be  at  least  as  old  as  the  reindeer,  must  n't  he  ? 
Agnes.     Of  course. 

Tom.  And  if  the  fossil  reindeer  are  found  in  rocks  that  it 
took  5000  years  at  least  to  make,  then  the  man  must  have 
lived  at  least  5000  years  ago.  That  is  the  way  they  find  out. 

Jack.  That  is  the  way 
they  find  out,  —  yes,  Tom  ; 
but  you  must  remember 
that  just  about  5000  years 
ago,  in  Egypt,  men  were 
building  palaces  and  tem- 
ples and  pyramids,  writing 
letters  to  each  other,  keep- 
ing accounts,  spinning  and 
weaving,  painting,  and 


FIG.  191 


making  statues.  You  have 
to  go  back  at  least  100,000 
years  to  find  the  earliest  men.  Agnes,  there  is  a  place  in 
the  West  —  Idaho  or  California,  I  forget  which  —  where  they 
lately  found  something  very  like  a  doll ;  it  might  have  been 


PHYSIOGRAPHY 


213 


an  idol,  but  it  looked  like  a  doll.     Now  this  doll  was  buried 

in  gravel  that  had  been  brought  down  by  an  old-time  river. 

No    one    knows    exactly   how  long    it   took  for    the   river   to 

bring  down  all  the  gravel  that  covered  the  place  where  the 

doll  was  dropped  by  the  man  who  had  it,  but    it  must  have 

taken    thousands    of    years.      Then, 

long  afterwards,  the  volcanoes  near 

by  sent  out  rivers  of  lava,  and  thick 

sheets   of  the  lava  poured  out   and 

covered  the  old  gravels  and  dried  up 

the  old  river.     No  one  knows  exactly 

how  many  thousands  of  years  it  took 

for  the  many  sheets  of  lava  to  form 

one  above  another  ;   but   they  were 

more  than  half  a  mile  thick  —  that 

we  know.     Then  came  a  new  river 

flowing  across  the  lava,  and  it  flowed 

for  so  many  thousand  years  that  it 

cut  a  deep  groove  for  its  bed  in  the 

hard  lava.     Scientific  men  can  make 

a  pretty  good  guess  how  long  each  of 

these  different   things   took.     Some 

men  were  sinking  a  deep  well  in  the 

valley  of  the  new  river  the  other  day, 

and  in  the  well,  deep  down,  they  found 

the  doll.     You  see  that  we  can  make 

a  pretty  good  guess  how  long  ago  the  doll  was  made  by  adding  up 

all  the  years  that  were  required  to  deposit  the  gravel,  and  to  make 

the  lava  sheet,  and  for  the  river  to  cut  its  way  in  the  lava. 

Agnes.    Yes,  I  see.     I  suppose  that  is  certainly  the  oldest 
doll  in  the  whole  world,  though. 


FIG.  192.  A  GEYSER  SPOUT- 
ING BOILING  WATER  WHICH 
COMES  FROM  DEEP  DOWN  IN 
THE  EARTH 


214 


THE  SCIENCES 


The  Internal  Heat  of  the  Earth.  —  "  You  were  saying,"  said 
Tom,  "that  the  interior  of  the  earth  is  made  of  melted  rock. 
I  suppose  you  know  that  by  the  melted  lava  which  comes  from 
volcanoes.  Lava  is  melted  rock." 

Jack.  Yes,  it  is  known  in  that  way  :  volcanoes  pour  out  melted 
rock.  And  then  geysers  send  out  hot  water  —  boiling  water 
sometimes ;  and  in  regions  where  there  are  no  volcanoes  we 


FIG.  193.    THE  PEAK  OF  TENERIFFE  IN  THE  CANARY  ISLANDS 

The  mountain  is  12,000  feet  high,  and  its  beautiful  form  has  been  shaped  by  the  lava  streams 
flowing  down  from  the  crater.  Notice  that  the  rocks  in  the  foreground  form  part  of  a 
very  much  larger  crater  that  was  active  in  ancient  times  and  is  now  extinct. 


find  that  the  deep  wells  always  send  out  hot  water  —  the 
deeper  the  well,  the  hotter  the  water. 

Fred.    How  deep  are  the  deepest  wells,  Jack  ? 

Jack.  There  are  some  in  Europe  nearly  a  mile  deep.  They 
are  not  dug,  •  you  know,  but  are  sunk  by  boring.  There 
are  deep  wells  in  America,  too  ;  one  in  St.  Louis  is  3800  feet 
deep  —  more  than  two  thirds  of  a  mile.  The  water  from  it  has 
a  temperature  of  105°.  Boiling  water  is  212°,  you  know. 


PHYSIOGRAPHY  215 

Volcanoes.  —  "  You  know  there  are  some  splendid  volcanoes 
in  Hawaii,"  said  Jack;  "papa'  has  seen  them.  One  of  them 
especially  is  easy  to  visit — Kilauea,1  they  call  it.  It  is  a  great 
lake  filled  with  red-hot  boiling  lava  that  comes  up  from  some 
reservoir  of  lava  deep  in  the  ground.  The  lava  is  liquid  rock. 
Usually  it  does  not  flow  over  the  rim  of  the  crater,  but  sometimes 
it  overflows  and  sends  great  streams  of  red-hot  lava  all  over  the 
country  round  about  and  even  as  far  as  the  sea  —  fifty  miles  off. 


FIG.  194 

A  volcano  is  built  up  somewhat  as  in  the  picture.  Underneath  it  are  old  rocks  in  layers. 
There  is  a  reservoir  of  lava  somewhere  underneath  them,  and  a  pipe  filled  with  lava 
leading  to  the  surface.  (The  lava  is  colored  black  in  the  picture.)  When  the  lava  overflows 
it  moves  down  the  side  of  the  mountain  like  a  great  river  and  covers  up  everything  that 
comes  in  its  way.  The  upper  end  of  the  pipe  is  the  vent,  and  the  lake  at  the  top  is  the 
crater.  There  is  often  more  than  one  vent.  (See  the  little  black  lines  in  the  picture 
leading  to  different  cones.) 

"  Vesuvius,  near  Naples,  is  the  most  famous  volcano.  You 
know  it  buried  two  whole  cities  once  —  Herculaneum  and 
Pompeii."  2 

Agnes.    Tell  us,  Jack. 

Jack.  Pompeii  was  a  kind  of  summer  resort  where  the 
Romans  used  to  go  for  pleasure.  It  was  a  pretty  little  town 
full  of  fine  houses,  temples,  shops,  and  so  forth,  not  far  from 

1  Pronounced  ke'-lou-a'a. 

2  Pronounced  pom-pa'ye. 


216  THE  SCIENCES 

the  volcano  of  Vesuvius.  Seventy-nine  years  after  Christ 
(A.D.  79)  there  was  a  great  eruption,  and  the  ashes  began  to 
fall  on  the  city.  At  first  the  people  were  not  very  much 
frightened,  but  pretty  soon  things  got  worse  and  worse,  and 
they  began  to  gather  up  their  movables  and  to  leave  the  city. 
A  great  many  of  them  got  away,  but  hundreds  and  hundreds 
were  buried  in  the  ashes  and  died  there.  The  ashes  kept  on 
falling  for  days,  and  the  whole  city  was  covered  up.  Almost 
the  same  thing  happened  in  Martinique  in  May,  1902.  Just 
imagine  what  might  happen  if  there  were  a  volcano  near  New 
York,  and  if  the  city  were  to  be  covered  up  with  a  thick  layer 
of  ashes  and  not  even  found  again  for  more  than  a  thousand 
years ! 

Agnes.    Not  found  for  a  thousand  years  ! 

Jack.  Well,  Pompeii  was  buried  in  A.D.  79,  and  it  was  not 
until  1748  that  people  began  to  dig  there  and  found  the  whole 
city  complete,  just  as  it  had  been  left  a  good  deal  more  than  a 
thousand  years  before. 

In  a  baker's  shop,  for  instance,  they  found  loaves  of  bread 
all  shriveled  up,  and  perfumes  and  oil  and  jewelry  in  other 
shops.  The  houses  were  filled  with  things  that  the  people 
used  every  day ;  everything  was  just  as  before. 

Agnes.  But  the  people,  Jack —  were  they  found  ?  Were  their 
bodies  found  ? 

Jack.  Their  bodies  had  mostly  wasted  away,  Agnes  ;  they 
found  their  skeletons.  One  man  had  come  back  after  his 
money,  and  other  people  after  their  jewels.  The  money  and 
jewels  were  found,  and  the  bones  of  the  persons  near  them. 
In  one  place  they  found  a  picture  of  a  watchdog  with  the 
sign,  Cave  canem  ;  that  means  —  what  does  it  mean,  Tom,  in 
English  ? 


PHYSIOGRAPHY 


217 


Tom.    It  means  "  Beware  of  the  dog  !" 

Jack.  Yes;  as  we  should  say  "Look  out  for  the  dog!"  A 
very  great  deal  of  what  we  know  about  ancient  pictures  and 
statues  we  learned  from  Pompeii. 

Fred.  If  New  York  were  buried  and  dug  up  a  thousand  years 
from  now,  the  people  of  that  time  would  know  how  we  lived. 


FIG.  195 

The  picture  shows  the  volcano  of  Vesuvius  as  it  appears  to-day,  and  in  the  foreground  a  part 
of  the  city  of  Herculaneum  after  the  layer  of  lava  has  been  taken  off.  Herculaneum 
was  covered  with  thick  ashy  mud  and  was  even  better  preserved  than  Pompeii,  which 
was  buried  in  showers  of  ashes.  Everything  in  it  was  found  exactly  as  it  was  left  — 
shops,  houses,  temples,  jewelry,  tools. 

Tom.    If  you  went  into  a  house,  you  would  know  just  what 
each  room  had  been  used  for  —  the  kitchen   and   the  dining 


2l8  THE  SCIENCES 

room  and  the  bedrooms  —  and  just  what  pictures  we  had  liked 
and  hung  on  our  walls,  and  what  books  we  read,  and  everything 
of  that  sort. 

Mary.  And  they  would  know  what  games  we  played —  tennis 
and  golf ;  and  they  might  find  Agnes'  dolls  and  mine. 

Agnes.  Just  as  we  found  the  doll  Jack  told  us  about  that 
was  buried  under  the  lava  in  California. 

Fred.    Are  there  any  volcanoes  in  the  United  States  ? 

Jack.  There  are  plenty  of  mountains  that  are  old  worn-out 
volcanoes,  and  a  few  that  are  still  active.  Mount  Shasta,  for 
instance,  in  California,  is  an  old  volcano,  and  there  are  active 
volcanoes  in  Alaska,  Hawaii,  and  the  Philippines.  You  children 
ought  to  recollect,  every  time  you  look  at  a  map,  that  a  very 
large  part  of  three  great  states  —  Washington,  Oregon,  and 
Idaho  —  is  nothing  but  an  old  lava  field.  A  good  part  of  the 
lava  is  3000,  even  4000  feet  thick,  and  it  covers  thousands  and 
thousands  of  square  miles.  All  that  lava  flowed  from  ancient 
volcanoes,  though  it  did  not  flow  all  at  one  time;  for  they 
find  the  lava  in  layers  with  ashes  and  soil  between,  and  in 
some  of  the  soil  they  find  petrified  tree  trunks. 

Tom.  That  shows  the  trees  had  time  to  grow  between  one 
lava  flow  and  the  next  one,  does  n't  it  ? 

Jack.  Yes,  and  it  gives  you  an  idea  how  long  it  took  to 
deposit  all  that  thickness  of  lava.  The  doll  I  told  Agnes 
about  was  found  in  this  very  lava  field. 

Earthquakes.  — "Do  earthquakes  come  from  volcanoes?"  said 
Fred. 

Jack.  There  are  always  earthquakes  wherever  there  are 
active  volcanoes,  Fred.  You  can  see  that  a  volcano  in  eruption 
which  has  energy  enough  to  throw  huge  stones  thousands  of 
feet  into  the  air  must  shake  all  the  ground  near  it  by  its 


PHYSIOGRAPHY  219 

explosions.  All  volcanoes  make  earthquakes,  but  very  many 
earthquakes  are  not  caused  by  volcanoes. 

Mary.    What  does  cause  them  then,  Jack  ? 

Jack.  Suppose  you  lay  a  book  flat  on  its  side,  Mary,  and 
imagine  that  the  book  is  part  of  a  layer  of  rock  that  was  once 
deposited  at  the  bottom  of  the  sea.  Now  take  another  book 
and  lay  it  flat  on  the  first  one.  That  stands  for  a  second  layer 
of  rock  —  perhaps  a  different  kind  of  rock  —  lying  over  the 
first  layer.  Now  you  know  the  crust  of  the  earth  is  moving 
slowly  all  the  time,  sometimes  up,  sometimes  down.  Sup- 
pose both  those  layers  of  rock  were  lifted  so  that  one  end  of 
them  was  higher  than  the  other.  Tilt  the  books,  Mary,  and 
keep  tilting  them,  and  see  what  happens. 

Mary.    Why,  one  book  slides  off  the  other.1 

Jack.  That  is  exactly  what  sometimes  happens  to  great  beds 
of  rock.  They  lie  flat  in  the  first  place.  Then  they  are  slowly 
tilted,  and  by  and  by  one  of  them  slides  a  little  —  a  very  little  — 
on  the  other.  Ten  million  tons  sliding  only  a  little  way  — 
an  inch  perhaps  —  will  make  a  terrible  shock  that  can  be  felt 
for  hundreds  of  miles  around.  The  Charleston  earthquake 
was  caused  in  just  that  way. 

The  geologists  say  that  the  layers  of  rock  underneath  South 
Carolina  lie  one  on  another  like  the  two  books,  and  the  earth- 
quake was  caused  by  the  sliding  of  the  layers.  The  rocks  I  am 
talking  about  were  deep  underground,  you  know.  When  they 
moved,  the  rest  of  the  rocks  moved,  too,  just  as  a  pile  of  bricks 
will  slide  when  you  move  some  of  the  bottom  ones ;  all  of 
them  moved.  A  good  part  of  Charleston  was  wrecked,  you 
know,  and  all  the  eastern  part  of  the  United  States  was  shaken 

1  The  simple  experiment  should  be  tried  in  the  schoolroom,  choosing  two 
books  with  smooth  covers. 


22O 


THE   SCIENCES 


more  or  less.  Why,  they  even  felt  the  shock  at  Boston,  at 
Toronto  in  Canada,  at  Chicago,  at  St.  Louis,  and  at  New 
Orleans.  The  shock  was  not  severe  there,  but  it  was  felt. 


FIG.  196.    THE  CHURCH  OF  SAINT  AUGUSTINE  IN  MANILA,  PHILIPPINE 
ISLANDS,  AFTER  THE  EARTHQUAKES  OF  JULY,  1880 

Tom.    Of  course  an  earthquake  is  weaker  and  weaker  the 
farther  you  go  away  from  the  center  of  it. 


PHYSIOGRAPHY 


221 


Jack.  Yes ;  like  the  little  water  waves  in  a  pond  when  you 
throw  in  a  stone.  That  is  a  "  waterquake,"  you  might  say. 
You  know  the  waves  are  larger  and  higher  at  the  center,  and 


FIG.  197.    VIEW  OF  PART  OF  CHARLESTON,  S.C.,  WRECKED  BY  THE 
EARTHQUAKE  OF  AUGUST,  1886 

become  smaller  as  they  move  out.  All  of  South  Carolina  was 
badly  shaken,  so  that  chimneys  fell.  The  shocks  were  strong 
enough  to  frighten  people  in  Georgia,  in  Ohio,  and  in 


222  THE  SCIENCES 

Pennsylvania,  and  they  were  felt  as  far  as  the  Mississippi 
River,  and  farther. 

Mary.    Were  many  people  killed,  Jack  ? 

Jack.  Only  a  few,  Mary.  They  ran  out  of  their  houses,  and 
lived  in  the  parks  for  several  days  till  the  shocks  were  over. 

Agnes.    Oh,  did  the  earthquake  last  for  days  ? 

Jack.  There  were  shocks  every  now  and  then  for  several 
days,  but  only  a  few  really  severe  ones.  You  see  it  took 
several  days  for  all  those  rocks  underground  to  settle  down  and 
be  quiet.  There  was  an  earthquake  in  the  Mississippi  Valley 
once  (181 1)  that  lasted  nearly  a  year.  The  people  camped  out 
of  doors  for  months  and  months. 

Agnes.    Might  we  have  an  earthquake  here,  Jack  ? 

Jack.  Certainly,  we  might ;  no  one  can  tell.  There  are  not 
many  earthquakes  in  the  eastern  part  of  the  country,  and  those 
that  we  have  are  usually  light ;  you  need  not  be  afraid  of 
them.  If  an  earthquake  comes,  go  out  of  doors  and  keep  away 
from  houses  —  that  is  all.  But  there  are  earthquakes  every- 
where —  light  ones.  You  boys  can  prove  it  if  you  want  to. 

Fred.    How  can  we  prove  it  ? 

Jack.  Get  some  pieces  of  nice  wood  —  red  cedar,  for 
instance  —  and  make  two  or  three  pyramids.  (See  Fig.  198.) 
Then  cut  off  a  little  of  the  top  of  each  one  of  them,  and  stand 
them  upside  down  in  a  steady  place  —  on  the  mantelpiece  of  a 
room  that  is  not  used  much,  for  example.  When  a  slight  earth- 
quake comes  —  one  too  slight  for  you  to  feel  perhaps  —  the 
house  will  be  shaken  and  the  mantelpiece,  too,  and  the  pyramid 
will  fall  on  one  of  its  sides.  Try  it. 

The  boys  did  try  it.  They  made  half  a  dozen  pyramids 
and  cut  off  a  little  of  the  top  of  each  one,  and  stood  them 
about  in  different  places  in  the  house  and  in  the  barn.  They 


PHYSIOGRAPHY  223 

often  would  find  one  of  them  fallen  on  its  side,  and  they 
usually  discovered  that  the  housemaid,  in  dusting,  had  caused 
that  particular  earthquake.  But  every  few  months  they  found 
all  the  little  pyramids  thrown  down,  and  most  of  them  lying  in 
one  direction  ;*and  then  they  knew  that  there  had  been  a  light 
shock  —  too  light  for  them  to  feel,  but  strong  enough  to  over- 
turn their  "  earthquake  detectors,"  as  they  called  them.  The 


FIG.  198.     PYRAMID 

direction  in  which  the  detectors  lay  on  their  sides  showed  the 
direction  in  which  the  earthquake  wave  was  moving  —  north 
and  south,  for  instance. 

The  Lisbon  Earthquake. —  "They  say  the  Lisbon  earthquake 
was  one  of  the  very  worst,"  said  Tom ;  "  do  you  know  about 
that,  Jack?" 

Jack.  It  was  one  of  the  worst,  certainly,  because  there  was 
not  only  an  earthquake,  but  a  great  sea  wave  too.  The  people 
ran  out  of  their  houses  to  take  refuge  in  the  churches,  and  then 
the  churches  fell  and  crushed  them.  Many  went  to  the  wharves 


224  THE   SCIENCES 

so  as  to  be  away  from  falling  walls,  and  a  huge  wave  from  the 
sea  —  eighty  feet  high,  they  say  —  rolled  in  and  drowned 
thousands  of  people. 

Fred.  A  wave  eighty  feet  high  !  What  made  it,  Jack?  Was 
it  a  part  of  the  earthquake  ? 

Jack.  No  doubt  the  level  of  the  sea  bottom  was  changed  some- 
how, and  the  water  rolled  in  like  a  great  wall.  That  often  occurs 
in  South  American  earthquakes.  A  strange  thing  happened 
to  one  of  our  war  vessels  once.  It  was  the  Wateree,  and  she 
was  at  anchor  in  the  bay  of  Iquique1  in  Peru  (1868).  All  of 
a  sudden  came  a  great  wave  from  the  sea  and  tossed  the 
ships  about  like  boats,  and  it  carried  the  Wateree  far  inland 
and  left  her  there  high  and  dry.  Think  of  it  —  one  of  our  war 
ships  with  all  her  guns  and  men  (no  one  was  hurt)  high  and 
dry  on  land  ! 

Fred.    What  did  they  do  ?     Could  they  get  her  off  ? 

Jack.  No ;  and  so  the  government  took  away  all  her  cannon 
and  everything  that  was  valuable,  and  sold  her  to  a  Spanish 
gentleman  for  a  summer  house ! 

Agnes.  I  think  that 's  funny.  A  man-of-war  for  a  summer 
house ! 

Jack.  That  is  not  the  funniest  part  of  it,  Agnes.  A  few 
years  later  there  came  another  great  sea  wave,  and  it  lifted  up 
the  Wateree  and  carried  her  a  long  way  farther  inland,  and 
there  she  is  now,  a  summer  house  for  a  different  family. 

1  Pronounced  e-ke'ka. 


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